QC may crash while updating project nodes

Steps to reproduce:

• start QC with clean settings, have a valid kit configured
• open some bigger project (used QC for this)
  • when opening (but not configuring) the project the both nodes first created (project & project file) are selectable
• hitting the Configure button now triggers the parse of the project files and should automatically switch to Edit view
• switching the selection now fast between the project and the project file and back continuously may crash QC when it tries to query the flags() of the project file node (FlatModel::flags() it gets an invalid Node with nodeForIndex() and crashes when trying to call asProjectNode())

Note: This happens for qmake and cmake based projects.