Small roundoff errors during UV editing can sometimes occur, most likely due to so-called "catastrophic cancellation".

Here we set a tolerance around zero when using Constrain-To-Bounds and UV Scaling.

The tolerance is set at one quarter of a texel, on a 65536x65536 texture.

TODO: If this fix holds, we should formalize the tolerance into the UV editing subsystem, perhaps as a helper function, and investigate where else it needs to be applied.