Comment out some chatty debug messages in SyncMsg for collision messages.
Don't send an updatedProperties message if there is no information in
the sync cache. The case where there was an update to an object and then
the object was deleted in the same tick causes the update sending code
to still have the update flag set but it cannot find the information in
the sync cache. The symptom was the receiver of the empty update message
to complain about it being empty.
This fix does not send the message if the sync cache info can't be found.