add default z value for canvas screenshots

ppfun-bridge/src/pixelplanet/index.js

@@ -80,7 +80,8 @@ export async function parseCanvasLinks(text) {
   }
   lastParse = curTime;
   lastCoords = coordsParts;
-  const [ canvasIdent, x, y, z ]  = coordsParts;
+  const [ canvasIdent, x, y ]  = coordsParts;
+  const z = coordsParts[3] || 16;
 
   const canvas = canvases.get(canvasIdent);
   const upperBound = canvas.size / 2 - 1;