[PATCH] btrfs-progs: receive: fix a segfault that free() an err value

[Wang Yugui <wangyugui@e16-tech.com>]

I noticed a segfault of 'btrfs receive'.
$ gdb
 #0  process_clone (path=0x23829d0 "after.s1.txt", offset=0, len=2097152, clone_uuid=<optimized out>,
    clone_ctransid=<optimized out>, clone_path=0x2382920 "after.s1.txt", clone_offset=0, user=0x7ffe21985ba0)
    at cmds/receive.c:793
793                     free(si->path);
(gdb) p si
$1 = (struct subvol_info *) 0xfffffffffffffffe

'si' was a ERR value here. so add the check of 'IS_ERR()' before 'free()'.

Signed-off-by: Wang Yugui <wangyugui@e16-tech.com>
---
 cmds/receive.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/cmds/receive.c b/cmds/receive.c
index d106e554..cada6343 100644
--- a/cmds/receive.c
+++ b/cmds/receive.c
@@ -789,8 +789,8 @@ static int process_clone(const char *path, u64 offset, u64 len,
 	}
 
 out:
-	if (si) {
-		free(si->path);
+	if (si && !IS_ERR(si)) {
+		if(si->path) free(si->path);
 		free(si);
 	}
 	if (clone_fd != -1)
-- 
2.36.2