Fix up any unsupported themes when read from settings

src/settings/controllers/ThemeController.js

@@ -0,0 +1,33 @@
+/*
+Copyright 2019 New Vector Ltd
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import SettingController from "./SettingController";
+
+const SUPPORTED_THEMES = [
+    "dharma",
+    "dark",
+];
+
+export default class ThemeController extends SettingController {
+    getValueOverride(level, roomId, calculatedValue, calculatedAtLevel) {
+        // Override in case some no longer supported theme is stored here
+        if (!SUPPORTED_THEMES.includes(calculatedValue)) {
+            return "dharma";
+        }
+
+        return null; // no override
+    }
+}