If the Modules view of the debugger is one of the enabled views
the command for fetching modules is triggered before the
PdbEngine could start up at all.
Ignore the respective command if the engine is currently requested
to start.

Change-Id: I509d122ecba4f3bde6b2139a519c9a12ac627c2f
Reviewed-by: hjk <hjk@qt.io>