Don't show a blank frame on app startup.
The wasm update request system supports two types of update
requests: Expose and UpdateRequest. It can happen that both
types of request are made for a single window, in which case
the current code prefers UpdateRequest, since those must be
delivered in order to keep QWindow in a consistent state.
However, if the window is visible but not yet exposed then
delivering the update request will not make the window paint
anything, and we end up with a blank frame.
Ideally this should be handled elsewhere and QWindow::requestUpdate()
should not be called for non-exposed windows, but in the
case does happen then sending an expose here allows us to
recover.
Change-Id: Ib53050c33ad1769ea9b9ad678896af15f87a7ecb
(cherry picked from commit 4c18ebbc1c)
Reviewed-by: Mikołaj Boc <Mikolaj.Boc@qt.io>
97c40bf5bf