Crash earlier if native external scanner overflows serialization buffer

Author: maxbrunsfeld

lib/src/parser.c

@@ -397,10 +397,12 @@ static unsigned ts_parser__external_scanner_serialize(
       self->lexer.debug_buffer
     );
   } else {
-    return self->language->external_scanner.serialize(
+    uint32_t length = self->language->external_scanner.serialize(
       self->external_scanner_payload,
       self->lexer.debug_buffer
     );
+    assert(length <= TREE_SITTER_SERIALIZATION_BUFFER_SIZE);
+    return length;
   }
 }