qmljs: fix projectInfoForPath and fileToPath mapping

m_fileToPath was not always updated correctly which lead
projectInfoForPath to return a wrong/invalid project info,
messing up the paths used by the code model.

Change-Id: If5e144f1ef2c7353b9077deb1b9c9aa9d1708651
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>
Reviewed-by: Fawzi Mohamed <fawzi.mohamed@theqtcompany.com>