bring isEmpty() semantics in line with qmake
bring isEmpty() semantics in line with qmake

qmake doesn't check if there is exactly one empty element - be it
because (theoretically) there can be no empty elements.

Change-Id: I603f2a472c02d270eafd1b3f6f9adae4349b3af0
Reviewed-by: Daniel Teske <d8a411aec9a206efedb4d45b75fe8d13f1e2b628@nokia.com>
Reviewed-by: Oswald Buddenhagen <6a8868beda3e139b5ac22b2534a23d3e6ba81819@nokia.com>

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