GDB: Mixed debugging: Attach to unstarted results in segfault of inferior

Not sure if this was ever working (or supported)

Steps to reproduce:

• create / open Quick Application and compile it
• trigger Debug -> Start Debugging -> Attach to Unstarted Application
• configure the dialog if necessary and 'Start Watching'
• run the built application (either by hitting 'Run' inside QC or from cmdline)

Current result:

• inferior segfaults

Expected result:

• debugger attaches to inferior (as it's done for none-mixed debugging)