[BUG] Incorrect implementation of MemoryStore

[WizzyGeek]

MemoryStore acquires a usage token from other rates even when acquiring a token has failed

uprate/uprate/store.py

Lines 145 to 162 in c86dd7d

	# Optimisations: We do not need to update every rate
	# that expires only the ones that don't have usage tokens.
	for use_dt, rate in zip(record, self.limit.rates):
	if use_dt[0] == 0:
	if (then := (use_dt[1] + rate.period)) <= now:
	# We have no tokens left but the rate has expired
	# so we reset it and acquire a token.
	use_dt[:] = [rate.uses - 1, now]
	elif (retry := then - now) > worst:
	# no tokens and the rate has time left to expire.
	worst = retry
	worst_rate = rate
	else:
	use_dt[0] -= 1
	if worst is False:
	return True, 0.0, None
	return False, worst, worst_rate

Fix:

1. Check if acquiring possible
2. Then acquire