UI: Save after creating default scene

When initializing with a default scene, save the data to ensure a file
is actually present when needed (such as for scene collections which may
need the file)

obs/window-basic-main.cpp

@@ -414,6 +414,7 @@ void OBSBasic::Load(const char *file)
 	BPtr<char> jsonData = os_quick_read_utf8_file(file);
 	if (!jsonData) {
 		CreateDefaultScene();
+		SaveProject();
 		return;
 	}