Kits: Compiler combo disabled

Steps to reproduce:

• make sure you have at least 1 Qt and 2 compilers in PATH (I've got /usr/lib/icecc/bin/gcc and /usr/bin/clang which are automatically listed in QC settings)
• start QC with clean settings (or -settingspath XYZ)
• go to Tools -> Options -> Build & Run -> Compilers
• check that both compilers have been detected
• switch to Kits page and check the default created kit

Current result:

• compiler combo is disabled

Expected result:

• compiler combo can be used (worked until 4334c119cfefb7ef41c)