Exit BeginPaintDelegated if d3d11 device is not set

ResizeDelegated can exit early if there was an issue with resizing the
window due to an invalid handle. In such an event, the d3d11 device and
other DirectX objects would not be set, resulting in a nullptr exception
when creating the staging texture. Therefore, exit BeginPaintDelegated
before attempting to create the staging texture if d3d11_device_context_
is not set.

Change-Id: I74907d74bfabdd317da38fe93d3f17f23271e8a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6312799
Commit-Queue: Sahir Vellani <sahir.vellani@microsoft.com>
Reviewed-by: Rafael Cintron <rafael.cintron@microsoft.com>
Reviewed-by: Sunny Sachanandani <sunnyps@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1426625}