Defensive programming: ensure no infinite COMPRESS_OK loops

There's a possible failure mode if we've screwed up in our compression backends: we might say "COMPRESS_OK" over and over, while not making any progress. The changes I'm suggesting in #22629 (moved) turn this possible bug into a possible infinite loop.

I don't think this failure mode actually exists today, but let's prevent it anyway, by treating a COMPRESS_OK that makes no progress as if it were an error, and a BUG.