[C] Use getMaxHealth() when determining if a wolf can be fed.  Fixes BUKKIT-3998

**The Issue:**
Currently, when determining if a wolf is able to be fed or not, it checks the wolf's health against a hard coded value of 20.0.  Obviously this is fine and dandy in Vanilla minecraft, however, in bukkit, when we change the MaxHealth value for a wolf, this results in them not being able to be healed all the way up.

**PR Breakdown:**
This PR simply changes the comparison to use a call to get maxhealth rather than use a hardcoded value.

**JIRA Ticket:**
https://bukkit.atlassian.net/browse/BUKKIT-3998