btrfs-progs: Fix NULL pointer when receive clone operation

btrfs-progs: Fix NULL pointer when receive clone operation

Regression introduced by a2f7af94abe4a3491ca1280a2ae1d63edc0d62ab
"btrfs-progs: subvol_uuid_search: return error encoded pointer"
IS_ERR() will only check if it's an error code, won't check if it's
NULL.  And for all the caller the commit modifies, it can return NULL
and makes cause segfault.

Fix it by introducing new IS_ERR_OR_NULL() macro, and for NULL pointer
and needs to return int case, convert NULL pointer to -ENOENT.

Reported-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Tested-by: Tsutomu Itoh <t-itoh@jp.fujitsu.com>
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>