btrfs: fix NULL pointer dereference in do_abort_log_replay()

Coverity reported a NULL pointer dereference issue (CID 1666756) in
do_abort_log_replay(). When btrfs_alloc_path() fails in
replay_one_buffer(), wc->subvol_path is NULL, but btrfs_abort_log_replay()
calls do_abort_log_replay() which unconditionally dereferences
wc->subvol_path when attempting to print debug information. Fix this by
adding a NULL check before dereferencing wc->subvol_path in
do_abort_log_replay().

Fixes: 2753e4917624 ("btrfs: dump detailed info and specific messages on log replay failures")
Reviewed-by: Filipe Manana <[e-mail]>
Signed-off-by: Suchit Karunakaran <[e-mail]>
Signed-off-by: Filipe Manana <[e-mail]>
Signed-off-by: David Sterba <[e-mail]>

fs/btrfs/tree-log.c

···
 
 	btrfs_abort_transaction(wc->trans, error);
 
-	if (wc->subvol_path->nodes[0]) {
+	if (wc->subvol_path && wc->subvol_path->nodes[0]) {
 		btrfs_crit(fs_info,
 			   "subvolume (root %llu) leaf currently being processed:",
 			   btrfs_root_id(wc->root));