... now that also empty cells are to be broadcasted.

Set dirty and broadcast only the effective data range as determined by Sort.

This is more a workaround, a cleaner solution would be to refactor the
SetDirty() algorithm to iterate only through broadcasters and use
AreaBroadcast() to notify area listeners.

However, this can also be easily backported to 4-3.

Change-Id: I6d68ca0088cec6a8328a3e93364ac928ef69babe