EXT_debug_utils label functions call a null ptr if there is no layers enabled.

[JordanLogan-AMD]

When trying to use CmdBeginDebugUtilsLabelEXT or any other label function from the EXT_debug_utils extenstion without a layer that intercepts the function, a null pointer is called.

Issue can be reproduced with the cube demo by removing the code that loads the validation layer and running with --validate

Exception thrown at 0x0000000000000000 in cube.exe: 0xC0000005: Access violation executing location 0x0000000000000000. occurred
>	vulkan-1.dll!CmdBeginDebugUtilsLabelEXT(VkCommandBuffer_T * commandBuffer, const VkDebugUtilsLabelEXT * pLabelInfo) Line 2079	C
 	cube.exe!demo_draw_build_cmd(demo * demo, VkCommandBuffer_T * cmd_buf) Line 751	C
 	cube.exe!demo_prepare(demo * demo) Line 2230	C
 	cube.exe!WinMain(HINSTANCE__ * hInstance, HINSTANCE__ * hPrevInstance, char * pCmdLine, int nCmdShow) Line 3815	C

[zeux]

I believe there was an attempt to fix this issue in 4b858b5 but the fix was incomplete.

Specifically, while vkCmdBeginDebugUtilsLabelEXT now correctly skips execution if no layer implements it, vkGetDeviceProcAddr returns NULL if no layer implements it. It seems like a full solution to this issue requires substituting a dummy thunk when vkGetDeviceProcAddr is used. cc @lenny-lunarg

[MarkY-LunarG]

This should now be resolved with #95. Can you please verify?

[zeux]

@MarkY-LunarG Thanks, I can confirm this is resolved in loader as of 1.1.92.

[MarkY-LunarG]

Thanks for verifying!