Datepicker: hidden input without sibling should use parent for position

If you have a datepicker bound to a hidden input (being invoked manually, in my case via click handler on an unrelated element) and the datepicker has no visible elements following it within its container, then _findPos will throw a null reference exception.

The problem is that _findPos looks at nextSibling until it finds a non-hidden one, but if this never happens obj will be null after the while loop. My solution was to walk up to the parent if no visible siblings could be found, which looks like this:

	_findPos: function(obj) {
		var inst = this._getInst(obj);
		var isRTL = this._get(inst, 'isRTL');
		while (obj && (obj.type == 'hidden' || obj.nodeType != 1 || $.expr.filters.hidden(obj))) {
			obj = obj[isRTL ? 'previousSibling' : 'nextSibling'] || obj.parentNode;
		}
		var position = $(obj).offset();
		return [position.left, position.top];
	},

The changed line being:

			obj = obj[isRTL ? 'previousSibling' : 'nextSibling'] || obj.parentNode;