game: process partial UPDATE_OBJECT packets when a block parse fails

Previously, if any single block in an SMSG_UPDATE_OBJECT packet failed
to parse (e.g. unusual spline flags), the entire packet was dropped and
all entities in it were lost. On busy zones with many CREATE_OBJECTs in
one packet, one bad NPC movement block would silently suppress all NPCs
that followed it in the same packet.

- parseUpdateObject: break instead of return false on block failure,
  so already-parsed blocks are returned to the caller
- handleUpdateObject: fall through to process partial data when parsing
  returns false but some blocks were successfully parsed

src/game/game_handler.cpp

@@ -7327,7 +7327,8 @@ void GameHandler::handleUpdateObject(network::Packet& packet) {
         static int updateObjErrors = 0;
         if (++updateObjErrors <= 5)
             LOG_WARNING("Failed to parse SMSG_UPDATE_OBJECT");
-        return;
+        if (data.blocks.empty()) return;
+        // Fall through: process any blocks that were successfully parsed before the failure.
     }
 
     auto extractPlayerAppearance = [&](const std::map<uint16_t, uint32_t>& fields,