user32: When repainting a static control with SS_BITMAP style, do not erase the background if there is no valid bitmap to paint.

ole32: Now that the consumer side of the clipboard separated from the main clipboard object, simplify the initialization code.

ole32: The consumer data object is not a singleton, but reflects the state of the clipboard when it was acquired.

This is somewhat different from how Windows behaves. Windows stores
two properties; an IID and an endpoint number.