find Target
Finds the target for this goal selector, trying all target finders currently in use until it finds one that returns a non-null target.
This is intended to be used by goals to easily find targets without having to search the finders manually.
This will return null if no target could be found. This could be because there are no target finders in use, or because none of the target finders produced a non-null target.
Return
the target, or null if no target could be found