Fix the synchronisation for Vulkan stereo rendering
Fix the synchronisation for Vulkan stereo rendering

The image ready semaphore should be waited on at the point that the rendering to
the swapchain is carried out, not at the point that the offscreen buffers are cleared.
This avoids the assertion that was occurring when the semaphore was waited on a second
time.  There is still some way to go to get this overall rendering structure working,
though.

StrayLightning/aeolius,StrayLightning/aeolius,StrayLightning/aeolius