[Crash] Player joins > Server crash when Playerdata is present in the Map download from the Market.

[Release 360729]

Summary: Crash on Player join
Impact: Crash!
Repro Steps:
1) Create a server
2) Ask for more then one friend to join your server.
Observed Results: Crash!

Assertion failed: The server shouldn't send a player twice!
Condition is false: false
Function: LegacyClientNetworkHandler::handle in C:\DarwinWork\10\s\handheld\project\VS2015\Minecraft\Minecraft.Client\..\..\..\..\src-client\common\client\network\LegacyClientNetworkHandler.cpp @ 328

Expected Results: No Crash
Note:
Its always the specific player that crashes the server, but when loading on other map the player changes.