Fix memory leak in [RecentsDataSource dataSource:didStateChange:]

The block passed into `[MXSession listenToEventsOfTypes:onEvent:]` is stored with a strong
reference in the `listenerBlock` property of `MXSessionEventListener`. The method also
returns the listener and it is then stored into the `roomTagsListenerByUserId` dictionary
on `self`. Since a strong reference to `self` is captured in the block that means the block
retains `self` (via the capture) and `self` retains the block (via `roomTagsListenerByUserId`)
so there is a memory leak.

The bug is most easily reproduced during testing #4168 which involves closing the current
and creating a new session.

Signed-off-by: Johannes Marbach <n0-0ne+github@mailbox.org>

Riot/Modules/Common/Recents/DataSources/RecentsDataSource.m

@@ -337,9 +337,12 @@ NSString *const kRecentsDataSourceTapOnDirectoryServerChange = @"kRecentsDataSou
         if ((aState == MXKDataSourceStateReady) && dataSource.mxSession.myUser.userId)
         {
             // Register the room tags updates to refresh the favorites order
+            MXWeakify(self);
             id roomTagsListener = [dataSource.mxSession listenToEventsOfTypes:@[kMXEventTypeStringRoomTag]
                                                                 onEvent:^(MXEvent *event, MXTimelineDirection direction, id customObject) {
 
+                                                                    MXStrongifyAndReturnIfNil(self);
+
                                                                     // Consider only live event
                                                                     if (direction == MXTimelineDirectionForwards)
                                                                     {