fix padding bug

engine.cc

@@ -334,6 +334,7 @@ void Engine::regexp() {
 
               char *part = (char *)malloc(substring_length+1);
               part = strncpy(part, (char *)substring_start, substring_length);
+              part[substring_length] = '\0';
 
               subs[i-1] = part;
               free(part);