Debugger: Add missing breaks in switch statements

Detected by GCC7

Change-Id: Ic4a1f0adac486d3f6d0f7da15b24e983c17225f3
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/plugins/debugger/qml/qmlcppengine.cpp

@@ -630,6 +630,7 @@ void QmlCppEngine::slaveEngineStateChanged
                 case InferiorRunRequested:
                     // can happen if qml engine was active
                     notifyInferiorRunFailed();
+                    break;
                 default:
                     CHECK_STATE(InferiorStopOk);
                     break;