small bugfix in roundPixels so it now also works smoothly with hires enabled

[stephanvermeire]

Sprites now move really with one pixel at a time then roundPixels=true exabled.

[ekelokorpi]

Thanks for the PR! All pull requests should go to the develop branch: https://github.com/ekelokorpi/panda-engine/tree/develop

Could you explain your code changes a bit? I'm not sure if i understand it correctly.

For example this new line:
tx = Math.round(tx * game.scale)/game.scale;

Now if the game.scale value is 2, that line would not change the value at all, so it's doing the rounding for nothing?

Example:
Math.round(1.5 * 2) / 2 would result value 1.5