added check for null pointer before fixing tokens after parsing is done

jsmn.c

@@ -289,12 +289,14 @@ int jsmn_parse(jsmn_parser *parser, const char *js, size_t len,
 		}
 	}
 
+	if (tokens != NULL) {
 		for (i = parser->toknext - 1; i >= 0; i--) {
 			/* Unmatched opened object or array */
 			if (tokens[i].start != -1 && tokens[i].end == -1) {
 				return JSMN_ERROR_PART;
 			}
 		}
+	}
 
 	return count;
 }