Internet Explorer cursor fix

Internet Explorer doesn't update cursor style if it is null or undefined.

Fix so that when the cursor is updated, the incoming is checked for truthiness.  If it is, use it, else keep it as an empty string.

Author: champasaur

src/easeljs/display/Stage.js

@@ -800,10 +800,11 @@ this.createjs = this.createjs||{};
 		var list = this._mouseOverTarget = [];
 
 		// generate ancestor list and check for cursor:
+		// Note: Internet Explorer won't update null or undefined cursor properties
 		t = target;
 		while (t) {
 			list.unshift(t);
-			if (!cursor) { cursor = t.cursor; }
+			if (!cursor && t.cursor) { cursor = t.cursor; }
 			t = t.parent;
 		}
 		this.canvas.style.cursor = cursor;