Allow empty needle in mb_substr_count

Author: Girgias

ext/mbstring/mbstring.c

@@ -2459,11 +2459,6 @@ PHP_FUNCTION(mb_substr_count)
 		RETURN_FALSE;
 	}
 
-	if (needle.len == 0) {
-		php_error_docref(NULL, E_WARNING, "Empty substring");
-		RETURN_FALSE;
-	}
-
 	n = mbfl_substr_count(&haystack, &needle);
 	if (!mbfl_is_error(n)) {
 		RETVAL_LONG(n);