Fix string offset signed int UB in jit as well

Author: nikic

ext/opcache/jit/zend_jit_helpers.c

@@ -610,7 +610,7 @@ static void ZEND_FASTCALL zend_jit_fetch_dim_str_r_helper(zval *container, zval
 		offset = Z_LVAL_P(dim);
 	}
 
-	if (UNEXPECTED(Z_STRLEN_P(container) < (size_t)((offset < 0) ? -offset : (offset + 1)))) {
+	if (UNEXPECTED(Z_STRLEN_P(container) < ((offset < 0) ? -(size_t)offset : ((size_t)offset + 1)))) {
 		zend_error(E_WARNING, "Uninitialized string offset: " ZEND_LONG_FMT, offset);
 		ZVAL_EMPTY_STRING(result);
 	} else {
@@ -658,7 +658,7 @@ static void ZEND_FASTCALL zend_jit_fetch_dim_str_is_helper(zval *container, zval
 		offset = Z_LVAL_P(dim);
 	}
 
-	if (UNEXPECTED(Z_STRLEN_P(container) < (size_t)((offset < 0) ? -offset : (offset + 1)))) {
+	if (UNEXPECTED(Z_STRLEN_P(container) < ((offset < 0) ? -(size_t)offset : ((size_t)offset + 1)))) {
 		ZVAL_NULL(result);
 	} else {
 		zend_uchar c;