[Blocking] World crashing on second attempt to load

Release_446687
Summary:
Loading up Minecraft for the first time I am able to load Monster Battle Arena just fine, if I close the world and open the same world again, it crashes.
Impact:
Crashes the world during normal operation of opening the world. This prevents Monster Battle Arena from being able to be released for 1.2
Repro Steps:
1. Open Monster Battle Arena
2. Close Monster Battle Arena
3. Open Monster Battle Arena

Observed Results:
Crash
Expected Results:
not crash

Screenshots/Videos Attached:
https://youtu.be/51HBRQF2bJs

End of the Debug log shows:
```
[5236:3020] - VERBOSE DATABASE BPE NewWritableFileC:/Users/Jigarbov/AppData/Local/Packages/Microsoft.MinecraftUWP_8wekyb3d8bbwe/LocalState/games/com.mojang/minecraftWorlds/lVMCAJtKAAA=/db/002017.ldb

[5236:6424] - INFO RENDER RMG: async load complete
[5236:6424] - INFO RENDER RMG: async load complete
[5236:6424] - ERROR SYSTEM Assertion failed: OOB on read operation
Condition is false: !(checkedNumber > mBuffer.length())
Function: ReadOnlyBinaryStream::read in C:\DarwinWork\3\s\handheld\project\VS2015\Minecraft\Minecraft.Shared\..\..\..\..\src\common\network\BinaryStream.cpp @ 70

```
Is cut off there in the log too.

Template given in slack to reproduce.