[texmap] Borders on rotating images are hidden/wrongly rendered with edge distance antialiasing

When TextureMapperGL has enabled edgeDistanceAntialiasing, the borders of the image fail to render properly, showing different artifacts. It is pretty obvious on circle images where the borders of the circle are exactly touching the image border.

This is reproducible at least in WebKit Qt and WebKit Gtk (though I expect it to also fail on WebKitEFL as it uses coordinated graphics).