fixed memory leaks and almost all undefined behaviour

tests/regression/result.c

@@ -24,5 +24,7 @@ char const* result_get_error_string(result_t result) {
             return "decompression error";
         case result_error_round_trip_error:
             return "round trip error";
+        default:
+            return "unknown error - " + result_get_error(result);
     }
 }