REG: Post-mortem debugging does not work if Creator is already running

1. Start Creator, register Creator for post-mortem debugging, keep it running.
2. Start a known-to-crash program, crash it.
3. When Windows asks, select "Debug" and then "Debug with Qt Creator".

This will result in one of the following behaviors:

1. A popup appears, stating: "Unable to send command line arguments to the already running instance. It appears to be not responding."
2. Nothing will happen. qtcdebugger.exe and the crashed program will keep running in the background.

If Creator is not running, it works fine.