Fixed odd roller bed behavior

- When attached to a roller bed, pixel_y is now manually incremented and
removed instead of hardcored. Might not do much unless the mob is
already offset for any reason (in which case it won't reset it)
- Fixed useless if clause that caused mobs to not have their pixel_y
reset on roller beds unless they unbuckled themslves
Merge pull request #1324 from dylanstrategie/Offset-Fix

Fixed odd roller bed behavior