udf: fix return value for non-recorded-allocated extents in udf_map_block()

When someone creates a corrupted UDF filesystem where symlink contains
other extent type than EXT_RECORDED_ALLOCATED, it can leads to a crash
like:

 Oops: general protection fault
 KASAN: maybe wild-memory-access
 RIP: 0010:page_get_link (fs/namei.c:6503)
 Call Trace:
  vfs_readlink (fs/namei.c:6419)
  do_readlinkat (fs/stat.c:583)
  __x64_sys_readlink (fs/stat.c:605 fs/stat.c:602 fs/stat.c:602)

This is because in this case udf_map_block() fails to convert return
value of inode_bmap() from 1 to 0. Returned '1' propagates through
udf_bread() all the way up to __page_get_link() where it ends up being
treated as a folio pointer with obvious results.

Move the reset to 0 line outside the if, so udf_map_block() returns either
0 or -errno, even if the extent type is not EXT_RECORDED_ALLOCATED.

Fixes: c226964ec786 ("udf: refactor inode_bmap() to handle error")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Tested-by: Xiang Mei <xmei5@asu.edu>
Signed-off-by: Giorgi Kobakhia <gkobakhi@asu.edu>
Link: https://patch.msgid.link/20260928200445.18722-1-gkobakhi@asu.edu
Signed-off-by: Jan Kara <jack@suse.cz>