smb3: fix corrupt path in subdirs on smb311 with posix

Signed-off-by: Steve French <[e-mail]>

fs/cifs/smb2misc.c

···
 #ifdef CONFIG_CIFS_SMB311
 	/* SMB311 POSIX extensions paths do not include leading slash */
 	else if (cifs_sb_master_tlink(cifs_sb) &&
-		 cifs_sb_master_tcon(cifs_sb)->posix_extensions) {
+		 cifs_sb_master_tcon(cifs_sb)->posix_extensions &&
+		 (from[0] == '/')) {
 		start_of_path = from + 1;
 	}
 #endif /* 311 */