I ran into a situation where user32 will call EndClipboardUpdate even though
the clipboard hasn't changed. It went something like this:
* Program A acquires the clipboard and adds some delay-rendered data.
* Program B requests data from the clipboard, causing program A to receive
  WM_RENDERFORMAT.
* Program A calls SetClipboardData to fulfill the request, setting
  bCBHasChanged to TRUE.
* Program C acquires the clipboard.
* Program A opens the clipboard to enumerate the formats. When it closes the
  clipboard, EndClipboardUpdate is called.
Signed-off-by: Vincent Povirk <vincent@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>