qt5 a11y: Skip attributes without value

Skip attributes with empty string value in
'Qt5AccessibleWidget::attributes'.

Besides not being a useful value, I also
got a crash using Accerciser to navigate in Calc's
"Format Cells" dialog -> "Font Effects" -> "Text Decoration"
-> "Overlining" -> "Overlining".

'Qt5AccessibleWidget::attributes' had returned
"font-family:;font-size:0pt;font-weight:normal;"
and 'AtSpiAdaptor::getAttributes' (from the Qt library)
aborts, since it splits the "font-family:" part at the colon,
then expects two substrings: one for the attribute name, one
for the value - but there was no value set:

    QString joined = interface->textInterface()->attributes(offset, &startOffset, &endOffset);
    const QStringList attributes = joined.split (QLatin1Char(';'), Qt::SkipEmptyParts, Qt::CaseSensitive);
    for (const QString &attr : attributes) {
        QStringList items;
        items = attr.split(QLatin1Char(':'), Qt::SkipEmptyParts, Qt::CaseSensitive);
->      AtSpiAttribute attribute = atspiTextAttribute(items[0], items[1]);
        if (!attribute.isNull())
            set[attribute.name] = attribute.value;
    }

The IAccessible2 spec for the "background-color" text attribute [1]
doesn't specify any default value to be used.

Backtrace:

    Thread 1 received signal SIGABRT, Aborted.
        __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
        50      ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
        (rr) bt
    #0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
    #1  0x00007f4dcd0bd537 in __GI_abort () at abort.c:79
    #2  0x00007f4dba7fd810 in qt_message_fatal(QtMsgType, QMessageLogContext const&, QString const&) (context=..., message=...) at global/qlogging.cpp:1914
    #3  0x00007f4dba7f9d48 in QMessageLogger::fatal(char const*, ...) const (this=0x7ffc30a4a6b0, msg=0x7f4dbab9ebb0 "ASSERT failure in %s: \"%s\", file %s, line %d") at global/qlogging.cpp:893
    #4  0x00007f4dba7f1484 in qt_assert_x(char const*, char const*, char const*, int) (where=0x7f4db778eb36 "QList<T>::operator[]", what=0x7f4db778eac8 "index out of range", file=0x7f4db778ea90 "../../../include/QtCore/../../src/corelib/tools/qlist.h", line=579)
            at global/qglobal.cpp:3366
    #5  0x00007f4db7736a65 in QList<QString>::operator[](int) (this=0x7ffc30a4a730, i=1) at ../../../include/QtCore/../../src/corelib/tools/qlist.h:579
    #6  0x00007f4db773017e in AtSpiAdaptor::getAttributes(QAccessibleInterface*, int, bool) const (this=0x557748f27800, interface=0x7f4d8c07cc30, offset=9, includeDefaults=true) at atspiadaptor.cpp:2059
    #7  0x00007f4db772cd74 in AtSpiAdaptor::textInterface(QAccessibleInterface*, QString const&, QDBusMessage const&, QDBusConnection const&) (this=0x557748f27800, interface=0x7f4d8c07cc30, function=..., message=..., connection=...) at atspiadaptor.cpp:1802
    #8  0x00007f4db77274f8 in AtSpiAdaptor::handleMessage(QDBusMessage const&, QDBusConnection const&) (this=0x557748f27800, message=..., connection=...) at atspiadaptor.cpp:1286
    #9  0x00007f4db7fe4d04 in QDBusConnectionPrivate::activateObject(QDBusConnectionPrivate::ObjectTreeNode&, QDBusMessage const&, int) (this=0x7f4d8c014b00, node=..., msg=..., pathStartPos=27) at qdbusintegrator.cpp:1458
    #10 0x00007f4db7fe58ca in QDBusActivateObjectEvent::placeMetaCall(QObject*) (this=0x557753615310) at qdbusintegrator.cpp:1617
    #11 0x00007f4dbaab3c66 in QObject::event(QEvent*) (this=0x557748f27800, e=0x557753615310) at kernel/qobject.cpp:1314
    #12 0x00007f4db96be845 in QApplicationPrivate::notify_helper(QObject*, QEvent*) (this=0x557747e30970, receiver=0x557748f27800, e=0x557753615310) at kernel/qapplication.cpp:3632
    #13 0x00007f4db96bbcfb in QApplication::notify(QObject*, QEvent*) (this=0x557747f1d8b0, receiver=0x557748f27800, e=0x557753615310) at kernel/qapplication.cpp:2972
    #14 0x00007f4dbaa70aba in QCoreApplication::notifyInternal2(QObject*, QEvent*) (receiver=0x557748f27800, event=0x557753615310) at kernel/qcoreapplication.cpp:1064
    #15 0x00007f4dbaa71452 in QCoreApplication::sendEvent(QObject*, QEvent*) (receiver=0x557748f27800, event=0x557753615310) at kernel/qcoreapplication.cpp:1462
    #16 0x00007f4dbaa7213a in QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*) (receiver=0x0, event_type=0, data=0x557747eff460) at kernel/qcoreapplication.cpp:1821
    #17 0x00007f4dbaa71acc in QCoreApplication::sendPostedEvents(QObject*, int) (receiver=0x0, event_type=0) at kernel/qcoreapplication.cpp:1680
    #18 0x00007f4dbaaff079 in postEventSourceDispatch(GSource*, GSourceFunc, gpointer) (s=0x557748056a30) at kernel/qeventdispatcher_glib.cpp:277
    #19 0x00007f4dbfe4ce6b in g_main_context_dispatch () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
    #20 0x00007f4dbfe4d118 in  () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
    #21 0x00007f4dbfe4d1cf in g_main_context_iteration () at /lib/x86_64-linux-gnu/libglib-2.0.so.0
    #22 0x00007f4dbaaff7a2 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x557748062a70, flags=...) at kernel/qeventdispatcher_glib.cpp:423
    #23 0x00007f4db76af8fc in QXcbGlibEventDispatcher::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (this=0x557748062a70, flags=...) at qxcbeventdispatcher.cpp:143
    #24 0x00007f4db9255353 in Qt5Instance::DoYield(bool, bool) (this=0x557747f22580, bWait=4, bHandleAllCurrentEvents=2) at .../libreoffice/vcl/qt5/Qt5Instance.cxx:400
    #25 0x00007f4db9255465 in Qt5Instance::AnyInput(VclInputFlags) (this=0xd87f0c9bbde3ed00, nType=(VclInputFlags::PAINT | VclInputFlags::TIMER | VclInputFlags::OTHER | VclInputFlags::APPEVENT | unknown: 0x7fc0))
            at .../libreoffice/vcl/qt5/Qt5Instance.cxx:422
    #26 0x00007f4dc594b64a in ImplYield(bool, bool) (i_bWait=true, i_bAllEvents=false) at .../libreoffice/vcl/source/app/svapp.cxx:465
    #27 0x00007f4dc594be0b in Application::Yield() () at .../libreoffice/vcl/source/app/svapp.cxx:532
    #28 0x00007f4dc594b357 in Application::Execute() () at .../libreoffice/vcl/source/app/svapp.cxx:444
    #29 0x00007f4dcd2c4226 in desktop::Desktop::Main() (this=0x7ffc30a4c540) at .../libreoffice/desktop/source/app/app.cxx:1602
    #30 0x00007f4dc5967cc6 in ImplSVMain() () at .../libreoffice/vcl/source/app/svmain.cxx:199
    #31 0x00007f4dc5967de7 in SVMain() () at .../libreoffice/vcl/source/app/svmain.cxx:231
    #32 0x00007f4dcd324e9f in soffice_main() () at .../libreoffice/desktop/source/app/sofficemain.cxx:98
    #33 0x000055774613895d in sal_main () at .../libreoffice/desktop/source/app/main.c:49
    #34 0x0000557746138943 in main (argc=2, argv=0x7ffc30a4c8b8) at .../libreoffice/desktop/source/app/main.c:47

[1] https://wiki.linuxfoundation.org/accessibility/iaccessible2/textattributes

Change-Id: I5e9d5121e69340ff728a87b4a6cb5c182d9ad11b
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/119247
Tested-by: Jenkins
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>

vcl/qt5/Qt5AccessibleWidget.cxx

@@ -873,12 +873,9 @@ QString Qt5AccessibleWidget::attributes(int offset, int* startOffset, int* endOf
             sAttribute = "font-weight";
             sValue = lcl_convertFontWeight(*o3tl::doAccess<double>(prop.Value));
         }
-        else
-        {
-            continue;
-        }
 
-        aRet += sAttribute + ":" + sValue + ";";
+        if (!sAttribute.isEmpty() && !sValue.isEmpty())
+            aRet += sAttribute + ":" + sValue + ";";
     }
     *startOffset = offset;
     *endOffset = offset + 1;