UI: If scene/source names exist, start from 2

Currently if you have a scene, "Scene" for example, and you create a new
scene, the dialog will pop up with a default name, but it'll start with
"Scene 1" instead of "Scene 2".  Same thing occurs with sources.  This
fixes that to start from 2 instead.

UI/window-basic-main.cpp

@@ -3051,7 +3051,7 @@ void OBSBasic::on_actionAddScene_triggered()
 	string name;
 	QString format{QTStr("Basic.Main.DefaultSceneName.Text")};
 
-	int i = 1;
+	int i = 2;
 	QString placeHolderText = format.arg(i);
 	obs_source_t *source = nullptr;
 	while ((source = obs_get_source_by_name(QT_TO_UTF8(placeHolderText)))) {