Fix load failure in firefox when indexedDB is disabled

src/vector/rageshake.js

@@ -410,8 +410,16 @@ module.exports = {
         }
         logger = new ConsoleLogger();
         logger.monkeyPatch(window.console);
-        if (window.indexedDB) {
-            store = new IndexedDBLogStore(window.indexedDB, logger);
+
+        // just *accessing* indexedDB throws an exception in firefox with
+        // indexeddb disabled.
+        let indexedDB;
+        try {
+            indexedDB = window.indexedDB;
+        } catch(e) {}
+
+        if (indexedDB) {
+            store = new IndexedDBLogStore(indexedDB, logger);
             initPromise = store.connect();
             return initPromise;
         }