Blur sphere + Crossfade = render artifacts

[Player701]

This issue happens with a very specific setup which depends on user settings as well as the game state, so I'm attaching my INI here to help reproduce the bug. Note that there may be other cases where this issue can manifest itself, but it all seems to happen when the level is loading.

Testing procedure:

1. Warp to any map.
2. Type "IDBEHOLDI" to get the blur sphere powerup.
3. Save the game.
4. Load the save. If "Screen wipe style" is set to "Crossfade", a rendering artifact will appear on the screen while the crossfade is happening. For me, it appears in the bottom area of the screen and looks like a thin black column spanning about 1/3 of the screen height.

Screenshot:


Git bisect shows that the issue started happening in this commit.

System information: NVIDIA GTX 660, Windows 7 64-bit.

[Graf Zahl]

It also happens only with the 'Noise' fuzz style. Looks like a bug in that shader function.