Plug lavapipe leaks.
We would like to run tests with AddressSanitizer/LeakSanitizer to find leaks on our code (it's waaaay faster than Valgrind.) Alas this raises red flags on leaks in Vulkan drivers leaks. NVIDIA and Intel Vulkan drivers have quite a few. But lavapipe is close to being clean of leaks.
This MR plugs two leaks found.