writeMap(): Adding ANGLE to directives saved

ANGLE is missing in the directives for the generated mapfile when calling mapfile.c:writeMap() ; this commit aims to force saving the custom angle.

Note: I could not manage to test it at runtime (compilation succeeded though), but due to the triviality of the PR, I thought it was ok to propose it in the current state. I checked that the map->gt object was created even with a blank mapfile.