boot loader: packagefs: Fix memory leak on unmount

The PackageNodes weren't destroyed.

src/system/boot/loader/file_systems/packagefs/packagefs.cpp

@@ -72,7 +72,7 @@ struct PackageNode : DoublyLinkedListLinkImpl<PackageNode> {
 		fModifiedTime.tv_nsec = 0;
 	}
 
-	~PackageNode()
+	virtual ~PackageNode()
 	{
 		free(fName);
 	}
@@ -194,6 +194,12 @@ struct PackageDirectory : PackageNode {
 	{
 	}
 
+	~PackageDirectory()
+	{
+		while (PackageNode* node = fEntries.RemoveHead())
+			delete node;
+	}
+
 	void AddChild(PackageNode* node)
 	{
 		fEntries.Add(node);