explorer: Initialise window->pidl to NULL in shellwindows_Register().

Since array_reserve() doesn't.

Signed-off-by: Henri Verbeet <hverbeet@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>

programs/explorer/desktop.c

@@ -1219,6 +1219,7 @@ static HRESULT WINAPI shellwindows_Register(IShellWindows *iface,
     window->hwnd = hwnd;
     window->class = class;
     *cookie = window->cookie = ++cookie_counter;
+    window->pidl = NULL;
 
     LeaveCriticalSection(&sw->cs);
     return S_OK;