ra: assert against unsigned underflow in q_total
ra: assert against unsigned underflow in q_total

q_total should never go below 0 (which is why it's defined as unsigned),
and if it does, then something is seriously wrong.

Signed-off-by: Connor Abbott <71178acffcc112b21e5858656e5751f5e4aa9364@gmail.com>
Reviewed-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>

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