Make do_exploding_wall_frame set WALL_BLASTED

Hostage doors misbehave after commit 5cc09c9:

https://github.com/dxx-rebirth/dxx-rebirth/commit/5cc09c974aadaa3f5f3fe0ce32a3fc186e960c63#commitcomment-3037382

Descent 1 set WALL_BLASTED in blast_blastable_wall, but Descent 2 set
WALL_BLASTED in do_exploding_wall_frame.  Commit 5cc09c9 broke exploding
walls because it removed the WALL_BLASTED logic from
blast_blastable_wall, but did not add it to do_exploding_wall_frame.

Reported-by: zico <zico@dxx-rebirth.com>