Wgpu: Triangle example has validation layer errors

[rukai]

These two validation layer errors are repeatedly displayed while running the the triangle example with the latest wgpu git master.
OS: Arch Linux
GPU: GTX 960
Driver: Nvidia proprietary driver, version 418

        [0] 0x56010ba02080, type: 6, name: NULL
ERROR 2019-03-28T08:00:06Z: gfx_backend_vulkan: [Validation]  [ VUID-vkBeginCommandBuffer-commandBuffer-00049 ] Object: 0x56010ba009a0 (Type = 6) | Calling vkBeginCommandBuffer() on active command buffer 56010ba009a0 before it has completed. You must check command buffer fence before this call. The Vulkan spec states: commandBuffer must not be in the recording or pending state. (https://www.khronos.org/registry/vulkan/specs/1.1-extensions/html/vkspec.html#VUID-vkBeginCommandBuffer-commandBuffer-00049)
VUID-vkBeginCommandBuffer-commandBuffer-00049(ERROR / SPEC): msgNum: 0 - Calling vkBeginCommandBuffer() on active command buffer 56010ba009a0 before it has completed. You must check command buffer fence before this call. The Vulkan spec states: commandBuffer must not be in the recording or pending state. (https://www.khronos.org/registry/vulkan/specs/1.1-extensions/html/vkspec.html#VUID-vkBeginCommandBuffer-commandBuffer-00049)
    Objects: 1

        [0] 0x56010ba009a0, type: 6, name: NULL
ERROR 2019-03-28T08:00:06Z: gfx_backend_vulkan: [Validation]  [ VUID-vkQueueSubmit-pCommandBuffers-00071 ] Object: VK_NULL_HANDLE (Type = 6) | Command Buffer 0x56010ba009a0 is already in use and is not marked for simultaneous use. The Vulkan spec states: If any element of the pCommandBuffers member of any element of pSubmits was not recorded with the VK_COMMAND_BUFFER_USAGE_SIMULTANEOUS_USE_BIT, it must not be in the pending state. (https://www.khronos.org/registry/vulkan/specs/1.1-extensions/html/vkspec.html#VUID-vkQueueSubmit-pCommandBuffers-00071)
VUID-vkQueueSubmit-pCommandBuffers-00071(ERROR / SPEC): msgNum: 0 - Command Buffer 0x56010ba009a0 is already in use and is not marked for simultaneous use. The Vulkan spec states: If any element of the pCommandBuffers member of any element of pSubmits was not recorded with the VK_COMMAND_BUFFER_USAGE_SIMULTANEOUS_USE_BIT, it must not be in the pending state. (https://www.khronos.org/registry/vulkan/specs/1.1-extensions/html/vkspec.html#VUID-vkQueueSubmit-pCommandBuffers-00071)
    Objects: 1

[kvark]

Thank you for filing! I also do notice the errors, and they are a bit surprising since at some recent point I thought we fixed all the things :) Anyhow, this definitely needs to be investigated.

[kvark]

@rukai so here is a strange thing. I clearly remember fixing this, but now looking at the git history I'm not seeing the fix. So it must have been lost during numerous patches I was producing at that time. My apologies about this!

Good news is, the problem is known, and fix is trivial - will be merged as a part of #114
With this in, I can run a complex app without any per-frame validation errors :tada:

[rukai]

This was resolved, thanks!