V8Debugger: Don't send watcher requests if qml engine has not stopped

This fixes a regression introduced in a8ebf535b829dac. We shouldn't
send watcher evaluation commands while the QML engine hasn't actually
stopped, because this might lead to an assert on the server side.

Task-number: QTCREATORBUG-13916
Change-Id: I300e2f73c0a1a03e0e6187a5357abeba408f72a0
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>

src/plugins/debugger/qml/qmlv8debuggerclient.cpp

@@ -954,6 +954,9 @@ void QmlV8DebuggerClient::executeDebuggerCommand(const QString &command)
 void QmlV8DebuggerClient::synchronizeWatchers(const QStringList &watchers)
 {
     SDEBUG(watchers);
+    if (d->engine->state() != InferiorStopOk)
+        return;
+
     foreach (const QString &exp, watchers) {
         StackHandler *stackHandler = d->engine->stackHandler();
         if (stackHandler->isContentsValid() && stackHandler->currentFrame().isUsable()) {