debugger: don't crash when telling a dead runcontrol about a pid

Change-Id: I1cf33f3587de2e8e35a74a15aa797539f2f58014
Reviewed-on: http://codereview.qt.nokia.com/318


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: hjk <qthjk@ovi.com>