lib: Fix get_next_timeout_expiry

If get_next_timeout_expiry() fails, and libusb_get_next_timeout()
has no timeouts or failed, fprint_timeout will not be set, and
we cannot compare it to libusb_timeout.

Exit early if both failed or have empty queues.
1 job for <span class="ref-name">wip/hadess/nbis-fixes</span> in 2 minutes and 22 seconds (queued for 8 minutes and 18 seconds)
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passed #43308
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00:02:22