DebuggerEngine: Avoid warning when aborting in EngineShutdownRequested state

Change-Id: Ib0e0a2bbf0fa7d109a3910d0814ec9edef130dc4
Reviewed-by: hjk <qthjk@ovi.com>

src/plugins/debugger/debuggerengine.cpp

@@ -1258,6 +1258,8 @@ void DebuggerEngine::quitDebugger()
     case EngineRunRequested:
         notifyEngineRunFailed();
         break;
+    case EngineShutdownRequested:
+        break;
     case EngineRunFailed:
     case DebuggerFinished:
         break;