Don't treat the last row in hidden as deleted if already mounted (#17206)

Already mounted rows that resuspend may be considered as part of a tail
if they're at the end. However, for purposes of the tail="..." option
they don't get deleted. We deal with that in cutOffTailIfNeeded.

However, if they're also the first to suspend in the "hidden" case, we have
a special case that deletes the actual rendered row. This needs to consider
if that row was already mounted or things go wrong.