wined3d: Do not fail swapchain creation in wined3d_swapchain_vk_init() if a Vulkan swapchain could not be created.

While far from ideal, we can still use swapchain_blit_gdi() to get
back-buffers to the screen.
Signed-off-by: Henri Verbeet <hverbeet@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>