QmakeProject: Fix crash on updating sources
QmakeProject: Fix crash on updating sources

ProFileCacheManager::discardFile(s) may remove an entry from
the ProfileCache only when it is unused (which is the case iff
ent->locker is zero).

Change-Id: I9df2079087af6bd0d35dd121db6222e8a6ec9389
Task-number: QTCREATORBUG-14730
Reviewed-by: Oswald Buddenhagen <6a8868beda3e139b5ac22b2534a23d3e6ba81819@theqtcompany.com>

martyone/sailfish-qtcreator,martyone/sailfish-qtcreator,xianian/qt-creator,xianian/qt-creator,xianian/qt-creator,martyone/sailfish-qtcreator,xianian/qt-creator,xianian/qt-creator,xianian/qt-creator,martyone/sailfish-qtcreator,martyone/sailfish-qtcreator,martyone/sailfish-qtcreator,martyone/sailfish-qtcreator,xianian/qt-creator,martyone/sailfish-qtcreator,xianian/qt-creator,xianian/qt-creator,martyone/sailfish-qtcreator