layers: LX581, Warn for null-region blits
layers: LX581, Warn for null-region blits

Parameters specifying the extents for VkCmdBlitImage are often
misinterpreted from the spec. Add warningis if the extents do not
specify a positively-sized area.

Change-Id: I11324dcf4523b094d7545f406d5f87a1145e0563

KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,elongbug/Vulkan-LoaderAndValidationLayers,elongbug/Vulkan-LoaderAndValidationLayers,elongbug/Vulkan-LoaderAndValidationLayers,elongbug/Vulkan-LoaderAndValidationLayers