Fixed an off-by-one array error in the process

Clang cleanup

"taking the absolute value of unsigned type 'unsigned int' has no effect"

using abs() on an unsigned should be nop,  replace them with (angle_t)()

Need someone to verify this does not break any game logic

See merge request !63

Ceiling lighting fix

The ceiling lighting linedef special (and anything else that changes ceiling lighting directly for sectors) works in software mode now.

See merge request !62