decklink-output-ui: Stop outputs when unloading

When closing OBS, sometimes it would crash if the Decklink outputs
were active.

UI/frontend-plugins/decklink-output-ui/decklink-ui-main.cpp

@@ -330,3 +330,12 @@ bool obs_module_load(void)
 
 	return true;
 }
+
+void obs_module_unload(void)
+{
+	if (preview_output_running)
+		preview_output_stop();
+
+	if (main_output_running)
+		output_stop();
+}