As per the spec, a room with m.room.name value that is absent, null or
empty should be treated as if there is no m.room.name event at all:
https://spec.matrix.org/v1.17/client-server-api/#mroomname
This fetches the full m.room.name event and checks the content.name
instead of only checking the existence of the m.room.name event. This
results in correctly sending heroes for those rooms.
Fixes: https://github.com/element-hq/synapse/issues/19447
Signed-off-by: Joe Groocock <me@frebib.net>