This commit fixes a problem which can be observed in d3d10core and d3d11
tests while a device is destroyed in test_swapchain_flip().

When a swapchain is destroyed all contexts associated with this
swapchain are destroyed. A context is destroyed even if it is active.
This might lead to using a destroyed context. In order to fix this the
destruction of context is delayed until leaving the last level.
Signed-off-by: Józef Kucia <jkucia@codeweavers.com>
Signed-off-by: Henri Verbeet <hverbeet@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>