Bug: Sorting fails to sort locations in context-less messages

[mrtryhard]

Operating system: Windows, Mac OS, Linux
qt-ts-tools version: 0.5.0
Problem's description:
Messages that are not within a context have issues where location are not sorted correctly.

Expected behavior / output:
Location should be sorted correctly: by filename first then by lines.

Sample problematic translation file

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE TS>
<TS version="2.1" language="de">
    <message>
        <source>contextLessMessage</source>
        <location line="456" filename="ui_main.cpp" />
        <location line="312" filename="ai_main.cpp" />
        <location line="300" filename="ai_main.cpp" />
        <location line="10" filename="ui_potato_viewer.cpp" />
        <comment>An example entry for contextLessMessage</comment>
        <translation type="unfinished"></translation>
    </message>
    <context>
        <name>UiContext</name>
        <message>
            <source>Name</source>
            <location line="456" filename="ui_main.cpp" />
            <location line="10" filename="ui_potato_viewer.cpp" />
            <location line="321" filename="ui_main.cpp" />
            <location line="11" filename="ui_potato_viewer.cpp" />
            <comment>An example entry for Name</comment>
            <translation type="unfinished"></translation>
        </message>
        <message>
            <location line="10" filename="ui_potato_viewer.cpp" />
            <location line="144" filename="ui_main.cpp" />
            <source>This is just a Sample</source>
            <translation>Dies ist nur ein Beispiel</translation>
        </message>
        <message>
            <source>Practice more</source>
            <translation type="unfinished"></translation>
        </message>
    </context>
    <context>
        <name>CodeContext</name>
        <message>
            <source>I am a message in which was written in Code</source>
            <translation type="unfinished"></translation>
        </message>
    </context>
</TS>

Sample expected / correct output file

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE TS>
<TS version="2.1" language="de">
    <context>
        <name>CodeContext</name>
        <message>
            <source>I am a message in which was written in Code</source>
            <translation type="unfinished"></translation>
        </message>
    </context>
    <context>
        <name>UiContext</name>
        <message>
            <source>This is just a Sample</source>
            <translation>
                Dies ist nur ein Beispiel
            </translation>
            <location filename="ui_main.cpp" line="144"></location>
            <location filename="ui_potato_viewer.cpp" line="10"></location>
        </message>
        <message>
            <source>Name</source>
            <translation type="unfinished"></translation>
            <location filename="ui_main.cpp" line="321"></location>
            <location filename="ui_main.cpp" line="456"></location>
            <location filename="ui_potato_viewer.cpp" line="10"></location>
            <location filename="ui_potato_viewer.cpp" line="11"></location>
            <comment>An example entry for Name</comment>
        </message>
        <message>
            <source>Practice more</source>
            <translation type="unfinished"></translation>
        </message>
    </context>
    <message>
        <source>contextLessMessage</source>
        <translation type="unfinished"></translation>
        <location filename="ai_main.cpp" line="300"></location>
        <location filename="ai_main.cpp" line="312"></location>
        <location filename="ui_main.cpp" line="456"></location>
        <location filename="ui_potato_viewer.cpp" line="10"></location>
        <comment>An example entry for contextLessMessage</comment>
    </message>
</TS>