VulkanContext: Ensure present queue family is valid before incrementing queueCreateInfoCount

[OatmealDome]

VulkanContext::CreateDevice() attempts to find appropriate graphics queue and present queue families. It will skip trying to find a present queue family if the surface is VK_NULL_HANDLE (headless mode). However, even if the present queue family isn't valid, queueCreateInfoCount will be set to 2 as long as the graphics queue family index isn't the same as the present queue family index (which it won't, as the default value is the number of queues).

This causes DolphinNoGUI in headless mode on macOS to crash, as MoltenVK would attempt to create an MVKQueue using an invalid configuration.