Clear the timeline when disclosing a web feed so that the previously loaded timeline articles aren't merged. Fixes #3485

iOS/SceneCoordinator.swift

@@ -1151,7 +1151,9 @@ class SceneCoordinator: NSObject, UndoableCommandRunner {
 
 		rebuildBackingStores(initialLoad: initialLoad, completion:  {
 			self.treeControllerDelegate.resetFilterExceptions()
+			self.selectFeed(nil) {
 				self.selectFeed(webFeed, animations: animations, completion: completion)
+			}
 		})
 		
 	}