GRIM/EMI: Fix bridge height check. See #842
GRIM/EMI: Remove bridge length check.
MATH: Return false in intersectLine2d if lines do not intersect.
GRIM/EMI: Always walk towards the target position in a straight line if possible.
GRIM/EMI: The walk destination may reside in multiple sectors, so don't choose a single end sector.

This fixes Elaine walking through Guybrush at the end of the first cutscene in the set gme.