Fix a number of minor code quality issues

Most of these are complaints from my IDE. Discovered by going through nearly every file looking for React warnings.

src/components/views/rooms/AppsDrawer.js

@@ -71,7 +71,7 @@ export default createReactClass({
             MatrixClientPeg.get().removeListener('RoomState.events', this.onRoomStateEvents);
         }
         WidgetEchoStore.removeListener('update', this._updateApps);
-        dis.unregister(this.dispatcherRef);
+        if (this.dispatcherRef) dis.unregister(this.dispatcherRef);
     },
 
     componentWillReceiveProps(newProps) {

src/components/views/rooms/RoomRecoveryReminder.js

@@ -61,7 +61,6 @@ export default class RoomRecoveryReminder extends React.PureComponent {
                 loading: false,
                 error: e,
             });
-            return;
         }
     }