layers: Abort logging if null debug_report ptr
layers: Abort logging if null debug_report ptr

If a layer were to only be enabled on the device chain
it would not have had a chance to allocate a debug_report
data structure. Just treat such cases as having debug_report
disabled.

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools