Update return value of pick() when miss to match comment

Comment says ID_NONE is returned for miss, but code actually returns false.
Meanwhile GUI and scaffolding are expected null.
Let's standardize on what the comment says and update GUI etc. to match.

Author: GarboMuffin

src/RenderWebGL.js

@@ -1365,7 +1365,7 @@ class RenderWebGL extends EventEmitter {
     pick (centerX, centerY, touchWidth, touchHeight, candidateIDs) {
         const bounds = this.clientSpaceToScratchBounds(centerX, centerY, touchWidth, touchHeight);
         if (bounds.left === -Infinity || bounds.bottom === -Infinity) {
-            return false;
+            return RenderConstants.ID_NONE;
         }
 
         candidateIDs = (candidateIDs || this._drawList).filter(id => {
@@ -1383,7 +1383,7 @@ class RenderWebGL extends EventEmitter {
             return false;
         });
         if (candidateIDs.length === 0) {
-            return false;
+            return RenderConstants.ID_NONE;
         }
 
         const hits = [];