Vulkan: Fix bad delete of swapchain.
Vulkan: Fix bad delete of swapchain.

We could end up deleting a dirty pointer if the driver set an
output value during a call to vkCreateSwapchainKHR that generates
an error. In practice this turned up in some edge cases with
SwiftShader. Fix this by using a temporary variable.

Bug: chromium:1079475
Change-Id: Ia40e1fac94cbd56fd3bb800a179bb38b7f11fa26
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2216292
Reviewed-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Reviewed-by: Geoff Lang <b6fc25fe0362055230985c05cbfa8adb741ccc0f@chromium.org>
Commit-Queue: Jamie Madill <7e492b4f1c8458024932de3ba475cbf015424c30@chromium.org>

ppy/angle,ppy/angle,ppy/angle,ppy/angle