Bug when giving other Jetpack than Creative-Jetpack in Creative-Mode

[bookking3000]

If you are in Creative-Mode and give yourself an Jetpack other than the Creative Jetpack then the Game will Crash as you can see in #139

The Jetpacks seems to be not registered, as you can see in #138 , when in Creative-Mode.

This causes an NullPointerException and makes the Game unable to load, because it will try to load the Jetpack in the Inventory everytime you start the World or Join a Server etc.