layers: Validate secondary command buffers are most recently bound.

Secondary cmd buffer bound to new primary cmd buffer cannot be submitted
under the first primary cmd buffer.

This is based on spec valid usage restriction in vkQueueSubmit:

Any given element of pCommandBuffers must not contain commands that execute a
secondary command buffer, if that secondary command buffer has been recorded in
another primary command buffer after it was recorded into this VkCommandBuffer
2 files changed