erofs-utils: lib: sync up zmap.c

erofs-utils: lib: sync up zmap.c

commit 31da107fdb0a ("erofs: fold in z_erofs_reload_indexes()")
commit 53a7f9961cdd ("erofs: clean up unnecessary code and comments")
commit 9ff471800b74 ("erofs: get rid of a useless DBG_BUGON")
commit cc4efd3dd2ac ("erofs: stop parsing non-compact HEAD index if clusterofs is invalid")
commit 118a8cf504d7 ("erofs: fix inconsistent per-file compression format")
commit 9b32b063be10 ("erofs: ensure m_llen is reset to 0 if metadata is invalid")

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20250206125034.1462966-5-hsiangkao@linux.alibaba.com