qmakeproject: fix crash when qtVersion is null
qmakeproject: fix crash when qtVersion is null

While it is not possible to create a qmake kit without qt, the qt
version might become invalid and be removed.

Change-Id: I99484c86d731ab5a47bff9bb1958158504617004
Reviewed-by: Friedemann Kleint <1b9f2592239daaec4856ccc1cfb4d2d55b35fb71@digia.com>
Reviewed-by: Eike Ziller <c142da16c73a95a82d35191bcc55b22835617128@digia.com>

xianian/qt-creator,Distrotech/qtcreator,kuba1/qtcreator,kuba1/qtcreator,xianian/qt-creator,AltarBeastiful/qt-creator,omniacreator/qtcreator,amyvmiwei/qt-creator,martyone/sailfish-qtcreator,maui-packages/qt-creator,colede/qtcreator,amyvmiwei/qt-creator,omniacreator/qtcreator,danimo/qt-creator,martyone/sailfish-qtcreator,colede/qtcreator,omniacreator/qtcreator,farseerri/git_code,colede/qtcreator,Distrotech/qtcreator,danimo/qt-creator,AltarBeastiful/qt-creator,omniacreator/qtcreator,maui-packages/qt-creator,Distrotech/qtcreator,omniacreator/qtcreator,amyvmiwei/qt-creator,danimo/qt-creator,farseerri/git_code,xianian/qt-creator,farseerri/git_code,Distrotech/qtcreator,martyone/sailfish-qtcreator,xianian/qt-creator,xianian/qt-creator,xianian/qt-creator,AltarBeastiful/qt-creator,farseerri/git_code,martyone/sailfish-qtcreator,maui-packages/qt-creator,maui-packages/qt-creator,AltarBeastiful/qt-creator,martyone/sailfish-qtcreator,kuba1/qtcreator,danimo/qt-creator,martyone/sailfish-qtcreator,kuba1/qtcreator,kuba1/qtcreator,farseerri/git_code,kuba1/qtcreator,kuba1/qtcreator,maui-packages/qt-creator,omniacreator/qtcreator,AltarBeastiful/qt-creator,farseerri/git_code,omniacreator/qtcreator,Distrotech/qtcreator,Distrotech/qtcreator,xianian/qt-creator,colede/qtcreator,danimo/qt-creator,kuba1/qtcreator,kuba1/qtcreator,farseerri/git_code,danimo/qt-creator,xianian/qt-creator,amyvmiwei/qt-creator,AltarBeastiful/qt-creator,colede/qtcreator,martyone/sailfish-qtcreator,amyvmiwei/qt-creator,danimo/qt-creator,AltarBeastiful/qt-creator,xianian/qt-creator,colede/qtcreator,AltarBeastiful/qt-creator,amyvmiwei/qt-creator,colede/qtcreator,martyone/sailfish-qtcreator,Distrotech/qtcreator,farseerri/git_code,martyone/sailfish-qtcreator,amyvmiwei/qt-creator,danimo/qt-creator,maui-packages/qt-creator,maui-packages/qt-creator,amyvmiwei/qt-creator,danimo/qt-creator