udf: refactor inode_bmap() to handle error

Refactor inode_bmap() to handle error since udf_next_aext() can return
error now. On situations like ftruncate, udf_extend_file() can now
detect errors and bail out early without resorting to checking for
particular offsets and assuming internal behavior of these functions.

Reported-by:  <syzbot+7a4842f0b1801230a989@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=7a4842f0b1801230a989


Tested-by:  <syzbot+7a4842f0b1801230a989@syzkaller.appspotmail.com>
Signed-off-by: Zhao Mengmeng <zhaomengmeng@kylinos.cn>
Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20241001115425.266556-4-zhaomzhao@126.com