Crash when building a CompilationDatabaseProjectManager project

Have opened a project using experimental CompilationDatabaseProjectManager plugin.

Sometimes when hitting build whole QtCreator crashes.

The build is done using custom steps that launches a shell script that builds whole c project.

The build script also invokes `bear` which updates compile_commands.json - not sure if thats a problem.

Have attached the stack trace of the crash...

I have attached a patch with possible fix/workaround.