cifs: missing null pointer check in cifs_mount

jira LE-1907
Rebuild_History Non-Buildable kernel-4.18.0-477.27.1.el8_8
commit-author Steve French <stfrench@microsoft.com>
commit 162004a

We weren't checking if tcon is null before setting dfs path,
although we check for null tcon in an earlier assignment statement.

Addresses-Coverity: 1476411 ("Dereference after null check")
	Signed-off-by: Steve French <stfrench@microsoft.com>
(cherry picked from commit 162004a)
	Signed-off-by: Jonathan Maple <jmaple@ciq.com>

Author: PlaidCat

fs/cifs/connect.c

@@ -3458,7 +3458,7 @@ int cifs_mount(struct cifs_sb_info *cifs_sb, struct smb3_fs_context *ctx)
 			rc = -ELOOP;
 	} while (rc == -EREMOTE);
 
-	if (rc)
+	if (rc || !tcon)
 		goto error;
 
 	kfree(ref_path);