fix: Select the skin in order to get bone count

At least in 3ds Max 2016, it is necessary to select the skin node
before being able to use any of the skin operations.

utils/exporters/max/ThreeJSAnimationExporter.ms

@@ -1303,6 +1303,7 @@ rollout ThreeJSExporter "ThreeJSExporter"
 			
 			max modify mode
 			
+			modPanel.setCurrentObject node.modifiers[#skin]
 			total_bones = skinops.getnumberbones node.modifiers[#skin]
 			
 			vertex_count = getNumverts node