Silence compiler warning.

Not all compilers understand that the elog(ERROR) never returns.

David Rowley

src/backend/libpq/crypt.c

@@ -160,6 +160,7 @@ encrypt_password(PasswordType target_type, const char *role,
 	 * handle every combination of source and target password types.
 	 */
 	elog(ERROR, "cannot encrypt password to requested type");
+	return NULL;		/* keep compiler quiet */
 }
 
 /*