Added null check for when material is null

Prevents null from being added to mods.BlockIdsRequiringAccessTrust and mods.BlockIdsRequiringContainerTrust
Added null check for when material is null

Prevent NullPointerException for when an ID is present on the block{} but never registered by the mod.
Added null check for when material is null

MaterialInfo.toString() can now return null values if the material doesn't exist. This null check prevents materials that return null from being added.
Merge pull request #25 from Jabulba/master

Check for ID's that return null materials and prevent them from being added.