Fix snapping when zoomed in `Polygon2D` UV editor

[kleonc]

After reading the code I concluded that uv_draw_ofs is not affected by the uv_draw_zoom, hence should be multpliplied by it as well when snapping. Also simplified some code when reading.

Fixes #94385.

Before (v4.3.rc2.official [3978628c6])	After (this PR)