Fix TT handling inside BLOCKQUOTE blocks (wikitext, 52ad5ee)

This was a corner case which was failing: a BLOCKQUOTE block with some text on one line (which starts a nested P block) followed by a new line (the P block continues) with a TT span.

We fix this by cleaning up the handling of excess element popping.

Signed-off-by: Greg Hurrell <greg@hurrell.net>