- turns out pj_transform will not always return an error code for
failed transforms and may instead just set values as HUGE_VAL
- this commit handles this and calls it an error by return false
from forward/backward
Arguably if `point_count` > 1 some values might be correctly transformed
while others might be HUGE_VAL. For the purposes of Mapnik we will consider
any HUGE_VAL as an error because we have no way to handle partial failures.
