Avoid potential integer overflow (php#18485)

Author: nielsdos

ext/intl/grapheme/grapheme_string.c

@@ -1053,8 +1053,8 @@ PHP_FUNCTION(grapheme_levenshtein)
 	}
 
 	zend_long *p1, *p2, *tmp;
-	p1 = safe_emalloc(strlen_2 + 1, sizeof(zend_long), 0);
-	p2 = safe_emalloc(strlen_2 + 1, sizeof(zend_long), 0);
+	p1 = safe_emalloc((size_t) strlen_2 + 1, sizeof(zend_long), 0);
+	p2 = safe_emalloc((size_t) strlen_2 + 1, sizeof(zend_long), 0);
 
 	for (i2 = 0; i2 <= strlen_2; i2++) {
 		p1[i2] = i2 * cost_ins;