Fill returning undefined vertices

[jhughes2112]

This tiny fix helps out when passing in a fill that doesn't appear to produce good output.

Stitch.Optimize = {
  joinPolylines: function (polylines, maxJoinDistance) {
-   let joinedPolylines = [polylines[0]];
+   //––– safety: drop falsy / empty polylines and short-circuit if nothing left
+   polylines = polylines.filter(p => p && p.vertices && p.vertices.length);
+   if (polylines.length === 0) return [];
+
+   let joinedPolylines = [polylines[0]];
    let queue = polylines.slice(1);

[jhughes2112]

    getBoundingBox() {
      let boundingBox = { min: new Stitch.Math.Vector(Infinity, Infinity), max: new Stitch.Math.Vector(-Infinity, -Infinity) };
      for (let vertex of this.vertices) 
	  {
        if (vertex.x < boundingBox.min.x) 
			boundingBox.min.x = vertex.x;
        else if (vertex.x > boundingBox.max.x) 
			boundingBox.max.x = vertex.x;
        if (vertex.y < boundingBox.min.y) 
			boundingBox.min.y = vertex.y;
        else if (vertex.y > boundingBox.max.y) 
			boundingBox.max.y = vertex.y;
      }
      boundingBox.width = boundingBox.max.x - boundingBox.min.x;
      boundingBox.height = boundingBox.max.y - boundingBox.min.y;
      boundingBox.center = boundingBox.min.add(new Stitch.Math.Vector(0.5 * boundingBox.width, 0.5 * boundingBox.height));
      return boundingBox;
    }

This also has a bug that causes fills to run forever in some cases. You can't do an if/else here, it can only be 4 ifs in the inner loop, otherwise there's a case where you have only 2 vertices and the first one is larger than the second one, you end up with -infinity or +infinity still in one of the bounding box coordinates. Just take out the else keywords.