Position: Guard against passing window to offset

Starting in jQuery 3.0 this will throw an error

Fixes #13493
Closes jquerygh-1565

(cherry picked from commit b3a9b13)

Author: arschmitz

ui/position.js

@@ -114,13 +114,14 @@ $.position = {
 	},
 	getWithinInfo: function( element ) {
 		var withinElement = $( element || window ),
-			isWindow = $.isWindow( withinElement[0] ),
-			isDocument = !!withinElement[ 0 ] && withinElement[ 0 ].nodeType === 9;
+			isWindow = $.isWindow( withinElement[ 0 ] ),
+			isDocument = !!withinElement[ 0 ] && withinElement[ 0 ].nodeType === 9,
+			hasOffset = !isWindow && !isDocument;
 		return {
 			element: withinElement,
 			isWindow: isWindow,
 			isDocument: isDocument,
-			offset: withinElement.offset() || { left: 0, top: 0 },
+			offset: hasOffset ? $( element ).offset() : { left: 0, top: 0 },
 			scrollLeft: withinElement.scrollLeft(),
 			scrollTop: withinElement.scrollTop(),