Try and handle removal of mods a bit better. Currently no way to allow a world which has missing
blocks to load - but i have the code in place to allow it i think.
Fix failing to load a world with missing mod blocks and items. There will be a way to force worlds to load
when stuff is missing, but for right now, it will fail as this is "world safe".
Some argumentation
Prevent player dat files getting reset during disconnects.

Since FML nulls out the player's playerNetServerHandler during login, we need to
make sure that writePlayerData does not attempt to overwrite the player's dat file
if the player disconnects during the "Logging In" process.