Avoid rendering both the background and window on the same line

[ccawley2011]

From what I understand, if the window is active on a given line it'll completely cover the background, so there's no need to draw both of them. In addition, this PR will only clear the buffer if neither the window nor the background are active, which improves performance a bit.

[deltabeard]

These changes causes failures in the DMG-Acid2 test as shown below.

Previously, the output was:

The left eye and the left chin are drawn by the background which is why they do not look correct after your changes (see https://github.com/mattcurrie/dmg-acid2?tab=readme-ov-file#eyes). The coordinates of the window can be changed to start at any x and y pixel. See https://gbdev.io/pandocs/Scrolling.html#ff4aff4b--wy-wx-window-y-position-x-position-plus-7 .

The increase in speed was impressive though. 🙂

[deltabeard]

As mentioned in the previous comment, the behaviour of the window is now not functioning correctly.