use QFileInfo to check if path is absolute to avoid assert on windows

on windos absolute path does not have to start with / . Remove failing assert
when editing ignored files list.

Signed-off-by: Matthieu Gallien <matthieu_gallien@yahoo.fr>

src/gui/accountsettings.cpp

@@ -385,8 +385,10 @@ void AccountSettings::slotEditCurrentLocalIgnoredFiles()
 
 void AccountSettings::openIgnoredFilesDialog(const QString & absFolderPath)
 {
-    Q_ASSERT(absFolderPath.startsWith('/'));
-    Q_ASSERT(absFolderPath.endsWith('/'));
+#if !defined QT_NO_DEBUG
+    QFileInfo folderPath(absFolderPath);
+    Q_ASSERT(folderPath.isAbsolute());
+#endif
 
     const QString ignoreFile = absFolderPath + ".sync-exclude.lst";
     auto layout = new QVBoxLayout();