Fix issue of wasm/aot file malformed format (#853)

Fix possible integer overflow unchecked issue when checking
wasm/aot file format.

core/iwasm/aot/aot_loader.c

@@ -90,7 +90,7 @@ static bool
 check_buf(const uint8 *buf, const uint8 *buf_end, uint32 length,
           char *error_buf, uint32 error_buf_size)
 {
-    if (buf + length > buf_end) {
+    if (buf + length < buf || buf + length > buf_end) {
         set_error_buf(error_buf, error_buf_size, "unexpect end");
         return false;
     }