Fix media timeline to load in encrypted rooms
When loading the timeline, the messages retrieved were always filtered
by the event type RoomMessage
and by those with URLs. However, when
encryption is used, the event type for all messages are
'RoomEncrypted' and the contents cannot be filtered by URL. The fix
changed to filter for events of type RoomEncrypted
when the room has
encryption enabled, and leaving the filter unchanged otherwise.
Fixes #1322 (closed).