Support widget forms with InheritSidebar

Currently the system assumes that if a widget ends up at "handleWidget" that the widget resides on the current page. This patch checks if we are inheriting the sidebar and if so finds the top level page with the widget.

code/controller/WidgetContentControllerExtension.php

@@ -28,11 +28,17 @@ class WidgetContentControllerExtension extends Extension {
 	public function handleWidget() {
 		$SQL_id = $this->owner->getRequest()->param('ID');
 		if(!$SQL_id) return false;
-
+
+		/** @var SiteTree $widgetOwner */
+		$widgetOwner = $this->owner->data();
+		while($widgetOwner->InheritSideBar && $widgetOwner->Parent()->exists()){
+			$widgetOwner = $widgetOwner->Parent();
+		}
+
 		// find WidgetArea relations
 		$widgetAreaRelations = array();
-		$hasOnes = $this->owner->data()->has_one();
-		
+		$hasOnes = $widgetOwner->has_one();
+
 		if(!$hasOnes) {
 			return false;
 		}
@@ -51,7 +57,8 @@ public function handleWidget() {
 				break;
 			}
 
-			$widget = $this->owner->data()->$widgetAreaRelation()->Widgets(
+
+			$widget = $widgetOwner->$widgetAreaRelation()->Widgets(
 				sprintf('"Widget"."ID" = %d', $SQL_id)
 			)->First();
 		}