Fix Divide-by-zero

potionEffect.getAmplifier() returns 0 for "Strength 1" and 1 for "Strength 2"
Change type comparison to string comparison

For some reason, my compiler doesn't like my comparing potion types directly, so I changed it to a string comparison.
Merge pull request #1 from roastnewt/master

Fixed Divide-by-Zero & Type Comparison