frontend: Use default location for user settings as fallback

When a unique path is set up as the location for user settings,
profiles, or scene collections, migrating the files from one computer
to another will lead to confusing error messages as the original paths
might not exist on the new machine.

The default directories for configuration files are already created by
this point, so using those paths as a fallback should enable OBS Studio
to also create the corresponding fallback settings files.

frontend/OBSApp.cpp

@@ -434,7 +434,7 @@ bool OBSApp::InitGlobalConfig()
 
 	uint32_t lastVersion = config_get_int(appConfig, "General", "LastVersion");
 
-	if (lastVersion < MAKE_SEMANTIC_VERSION(31, 0, 0)) {
+	if (lastVersion && lastVersion < MAKE_SEMANTIC_VERSION(31, 0, 0)) {
 		bool migratedUserSettings = config_get_bool(appConfig, "General", "Pre31Migrated");
 
 		if (!migratedUserSettings) {
@@ -448,19 +448,34 @@ bool OBSApp::InitGlobalConfig()
 	InitGlobalConfigDefaults();
 	InitGlobalLocationDefaults();
 
+	std::filesystem::path defaultUserConfigLocation =
+		std::filesystem::u8path(config_get_default_string(appConfig, "Locations", "Configuration"));
+	std::filesystem::path defaultUserScenesLocation =
+		std::filesystem::u8path(config_get_default_string(appConfig, "Locations", "SceneCollections"));
+	std::filesystem::path defaultUserProfilesLocation =
+		std::filesystem::u8path(config_get_default_string(appConfig, "Locations", "Profiles"));
+
 	if (IsPortableMode()) {
-		userConfigLocation =
-			std::filesystem::u8path(config_get_default_string(appConfig, "Locations", "Configuration"));
-		userScenesLocation =
-			std::filesystem::u8path(config_get_default_string(appConfig, "Locations", "SceneCollections"));
-		userProfilesLocation =
-			std::filesystem::u8path(config_get_default_string(appConfig, "Locations", "Profiles"));
+		userConfigLocation = std::move(defaultUserConfigLocation);
+		userScenesLocation = std::move(defaultUserScenesLocation);
+		userProfilesLocation = std::move(defaultUserProfilesLocation);
 	} else {
-		userConfigLocation =
+		std::filesystem::path currentUserConfigLocation =
 			std::filesystem::u8path(config_get_string(appConfig, "Locations", "Configuration"));
-		userScenesLocation =
+		std::filesystem::path currentUserScenesLocation =
 			std::filesystem::u8path(config_get_string(appConfig, "Locations", "SceneCollections"));
-		userProfilesLocation = std::filesystem::u8path(config_get_string(appConfig, "Locations", "Profiles"));
+		std::filesystem::path currentUserProfilesLocation =
+			std::filesystem::u8path(config_get_string(appConfig, "Locations", "Profiles"));
+
+		userConfigLocation = (std::filesystem::exists(currentUserConfigLocation))
+					     ? std::move(currentUserConfigLocation)
+					     : std::move(defaultUserConfigLocation);
+		userScenesLocation = (std::filesystem::exists(currentUserScenesLocation))
+					     ? std::move(currentUserScenesLocation)
+					     : std::move(defaultUserScenesLocation);
+		userProfilesLocation = (std::filesystem::exists(currentUserProfilesLocation))
+					       ? std::move(currentUserProfilesLocation)
+					       : std::move(defaultUserProfilesLocation);
 	}
 
 	bool userConfigResult = InitUserConfig(userConfigLocation, lastVersion);