UI: Fix issue from stream settings Qt slots refactor

5a40934 refactored slots around services but a
on_service_currentIndexChanged() was not replaced by ServiceChanged().

The latter contains the code that was in the former before the refactor.

https://github.com/obsproject/obs-studio/commit/5a409347d5bf7dec50c41641660a131c265fb4ad

UI/window-basic-settings-stream.cpp

@@ -170,7 +170,7 @@ void OBSBasicSettings::LoadStream1Settings()
 	ui->key->setText(key);
 
 	lastService.clear();
-	on_service_currentIndexChanged(0);
+	ServiceChanged();
 
 	UpdateKeyLink();
 	UpdateMoreInfoLink();