Fix scalelight[] memory leak

[JNechaevsky]

This fixes memory leak (over-consumption) by toggling detail mode or changing screen size. Few remarks:

• Probably not worth a comment, as this is our own code not a Chocolate one.
• Nothing for Heretic & Hexen since there is not smooth diminished lighting. It's a must have for TrueColor to be honest, but I'm not sure how to fit it in Crispness menu.
• This approach is pretty much same to Woof one.

Small note - it was barely possible to notice a leak while non-TrueColor build, obliviously because of smaller lighttable_t size. However, while experimenting with colored lighting and having 28 extra colormaps (both scalelight and zlight, TrueColor only approach), such leak costs about ~400 kilobytes every time R_ExecuteSetViewSize was hit! Never thought such experiments will be that useful. 🙂

[fabiangreffrath]

Thank you!