Fix zend_string_release

Author: youkidearitai

ext/mbstring/mbstring.c

@@ -2971,12 +2971,12 @@ static void php_mb_ulcfirst(INTERNAL_FUNCTION_PARAMETERS, php_case_mode mode)
 	zend_string *first = mb_get_substr(str, 0, 1, enc);
 	zend_string *second = mb_get_substr(str, 1, MBFL_SUBSTR_UNTIL_END, enc);
 	zend_string *head = mbstring_convert_case(mode, ZSTR_VAL(first), ZSTR_LEN(first), enc);
-	zend_string_release_ex(first, false);
 
 	if (zend_string_equals(first, head)) {
 		RETVAL_STR(zend_string_copy(str));
 	}
 
+	zend_string_release_ex(first, false);
 	zend_string *retval = zend_string_concat2(ZSTR_VAL(head), ZSTR_LEN(head), ZSTR_VAL(second), ZSTR_LEN(second));
 	zend_string_release_ex(head, false);
 	zend_string_release_ex(second, false);