[REG 4.4 -> 4.5] Crash when removing kit

1. Have Qt 5.9.1 in your PATH variable.
2. Start Creator with empty settings, e.g. by passing the parameters "-settingspath <empty dir>"
   Creator will automatically create a kit for the Qt version in PATH.
3. Create a new Qt Console Application using defaults.
4. Go to "Tools" -> "Options..." -> "Build & Run" -> "Kits".
5. Remove the Kit and click OK.
   Creator crashes.

Creator should not crash. Creator 4.4 survives this situation.

Found by Squish test tst_remove_kits