Prevent deletePixel splicing of index -1 as a cause of ghost pixels

when this happens, pixels are "deleted" starting from the newest pixel created and become ghost pixels present in pixelMap but not currentPixels (in worldgen worlds, this manifests as the pixels disappearing from the upwards and leftwards from the bottom right)

index.html

@@ -7000,7 +7000,7 @@
         }
         function deletePixel(x,y) {
             // remove pixelMap[x][y] from currentPixels
-            currentPixels.splice(currentPixels.indexOf(pixelMap[x][y]),1);
+            if(currentPixels.indexOf(pixelMap[x][y]) !== -1) { currentPixels.splice(currentPixels.indexOf(pixelMap[x][y]),1) };
             if (pixelMap[x][y]) {pixelMap[x][y].del = true;}
             delete pixelMap[x][y];
             /*for (var i = 0; i < currentPixels.length; i++) {