StudoPlugin: Add QTC_ASSERT to avoid empty project names

There have been issues with invalid properties in the telemetry backend.

Change-Id: I8ddd7740e927e83b363a8d5a87a24836ca573c73
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>

src/plugins/studiowelcome/studiowelcomeplugin.cpp

@@ -241,6 +241,7 @@ public:
                                  const QString &formFile,
                                  const QString &explicitQmlproject)
     {
+        QTC_ASSERT(!exampleName.isEmpty(), return );
         QmlDesigner::QmlDesignerPlugin::emitUsageStatistics("exampleOpened:"
                                                             + exampleName);