ProjectExplorer: Unconfigured project crashes QC on close

Steps to reproduce:

• have a developer build of Qt5
• start QC with clean settings (and without having a Qt in path)
• open qtbase.pro of the developer build Qt5
  • QC will bring you to the Projects view, providing a (temporary) Qt for this project
• do not click on 'Configure Project' - just switch to Edit mode
• close QC

Current result:

• QC crashes

Note: I tried with other projects but failed to reproduce.. The only way was to use qtbase of an already done developer build..