Fix length to copy

Author: weltling

Zend/zend_API.c

@@ -3001,7 +3001,7 @@ static zend_always_inline int zend_is_callable_check_func(int check_flags, zval
 		if (UNEXPECTED(Z_STRVAL_P(callable)[0] == '\\')) {
 			/* Skip leading \ */
 			ZSTR_ALLOCA_ALLOC(lmname, Z_STRLEN_P(callable) - 1, use_heap);
-			zend_str_tolower_copy(ZSTR_VAL(lmname), Z_STRVAL_P(callable) + 1, Z_STRLEN_P(callable));
+			zend_str_tolower_copy(ZSTR_VAL(lmname), Z_STRVAL_P(callable) + 1, Z_STRLEN_P(callable) - 1);
 			func = zend_fetch_function(lmname);
 			ZSTR_ALLOCA_FREE(lmname, use_heap);
 		} else {