reftests: Fix random failures of reftest

reftests: Fix random failures of reftest

The reftest is testing "transparent" works as expected by drawing a
purple background once with purple and once with transparent and
expecting the same result. This works fine unless anti-aliasing happens
at rounded corners. The overdraw of the 2nd background changes the
antialiased pixels.

Fix this by explicitly setting the border radius to 0.

Also reindent the file to make it more readable.