Aderoian

### Impact An attacker could crash PocketMine-MP by sending malformed JSON in `LoginPacket`. This happened due to a bug in [`netresearch/jsonmapper`](https://github.com/cweiske/JsonMapper). The library wasn't doing proper checks when mapping JSON arrays and objects onto scalar model properties such as strings. ### Patches The problem was fixed in a fork of JsonMapper in dktapps/JsonMapper@a31902a31f5b6fdb832f57c0e3a3f16a3b41c012. PocketMine-MP releases 4.20.5 and 4.21.1 have been released with the fix. ### Workarounds - Users of PocketMine-MP source installations may manually install the patched version of JsonMapper by backporting commit pmmp/PocketMine-MP@09668a37d66c6023685a948b7550c918620e98f2. - A plugin may also be able to workaround this issue by using `DataPacketReceiveEvent` to attempt detection of suspicious payloads. An `ErrorException` will be thrown in the crash case, which can be caught by plugins. ### References cweiske/jsonmapper#210