Food Infusion Fix

An exception is thrown if the itemstack does not have a tag compound.
Have altered the code to use method calls instead. This was found when
using the NEI mod, a blank name would be returned because of the
exception.
1. Added getInfusion method.
2. Used IsInfused and getInfusion methods.
Merge pull request #723 from Bletch1971/Food-Infusion-Fix

Added null check to infusion NBT tag.