Draw the ion blast's warp to the view's edge

FixedPlanned for 0.1.0

An ion cannon blast against the bottom of the view now warps the scene all the way to the view’s edge. The drawer kept a seven-row margin above the bottom that the original code needed because nothing else kept the warp’s fetches inside the view, and that margin showed as an undisturbed band across a blast at the view’s edge. With the fetches held inside the view where they are taken, the margin protected nothing and is gone. In the lowest rows a fetch from below would leave the view, so those pixels are left alone and the warp quiets toward the edge.

Credit: ZivDero