v3dv: handle the case where we fail to allocate a new job gracefully

v3dv: handle the case where we fail to allocate a new job gracefully

There are a handful of tests that simulate 'out of memory' situations
during swapchain image creation, and these can lead to failed job
allocations when the driver is running on the prime blit path, as that
involves creating a command buffer. The tests expect us to handle this
scenario gracefully and return an appropriate OOM error as a result.
This make sure we don't try to dereference a job if we failed to allocate
it so we don't crash and can return the OOM error gracefully in the
process.

Fixes:
dEQP-VK.wsi.xlib.swapchain.simulate_oom.*

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6766>