Ownership estimate overlay is flickery

[gjm11]

I'm using Lizzie with KataGo and find that the ownership estimate display is flickery; sometimes it briefly disappears altogether, sometimes it briefly displays in a distorted way.

I believe this is because BoardRenderer.drawEstimateRectKata is operating directly on the same BufferedImage that's used in actual rendering, and if BoardRenderer.draw happens to be called while it's being updated then bad things can happen. (Some or all of the ownership-indicators will be missing, and I guess the unsightly corrupted versions I see sometimes occur when draw is called while fillRect is doing its thing.) The flickering goes away completely if I make drawEstimateRectKata do this:

BufferedImage newEstimateImage = new BufferedImage(boardWidth, boardHeight, TYPE_INT_ARGB);
Graphics2D g = newEstimateImage.createGraphics();

// (actual code to recreate the image is here, same as before)

cachedEsitmateRectImage = newEstimateImage;