Engine: Wrong sprite rendering order in classic mode, where sprites are in close proximity to maskwalls

Found by MetHy.

Sprites that are in close proximity to a maskwall appear to suffer from some sort of rendering issue where they are drawn behind sprites that are further away. It doesn't seem to matter how far the camera is away from the sprite.

This does not occur in Polymost.

Examples:

In addition, sprites may also be drawn in front of a maskwall when they are actually behind it. Happens in Rednukem as well:

Test Map: MASKWALL.map

The RR instance can be reproduced in the first level, near the hidden moonshine.