cifs: check for NULL session password

It's possible for a cifsSesInfo struct to have a NULL password, so we
need to check for that prior to running strncmp on it.

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

fs/cifs/connect.c

···
 				    MAX_USERNAME_SIZE))
 				continue;
 			if (strlen(vol->username) != 0 &&
+			    ses->password != NULL &&
 			    strncmp(ses->password,
 				    vol->password ? vol->password : "",
 				    MAX_PASSWORD_SIZE))