adding edge case to _test_nonstandard_decimals_lp()

[jrhea]

this no longer results in negative interest. resolves #665

[github-actions]

Hyperdrive Gas Benchmark

Benchmark suite	Current: 110f17a	Previous: 6b3cb74	Deviation	Status
addLiquidity: min	1633 gas	1633 gas	0%	🟰
addLiquidity: avg	65025 gas	66020 gas	-1.5071%	✅
addLiquidity: max	291577 gas	305468 gas	-4.5474%	✅
checkpoint: min	1150 gas	1150 gas	0%	🟰
checkpoint: avg	47785 gas	47785 gas	0%	🟰
checkpoint: max	190769 gas	190992 gas	-0.1168%	✅
closeLong: min	1558 gas	1558 gas	0%	🟰
closeLong: avg	28111 gas	28159 gas	-0.1705%	✅
closeLong: max	150962 gas	151185 gas	-0.1475%	✅
closeShort: min	1549 gas	1549 gas	0%	🟰
closeShort: avg	29804 gas	29829 gas	-0.0838%	✅
closeShort: max	125358 gas	147421 gas	-14.9660%	✅
initialize: min	1582 gas	1582 gas	0%	🟰
initialize: avg	213244 gas	213204 gas	0.0188%	🚨
initialize: max	255056 gas	255056 gas	0%	🟰
openLong: min	1487 gas	1487 gas	0%	🟰
openLong: avg	50454 gas	50347 gas	0.2125%	🚨
openLong: max	184813 gas	185024 gas	-0.1140%	✅
openShort: min	1608 gas	1608 gas	0%	🟰
openShort: avg	49943 gas	49607 gas	0.6773%	🚨
openShort: max	180216 gas	179974 gas	0.1345%	🚨
redeemWithdrawalShares: min	1575 gas	1575 gas	0%	🟰
redeemWithdrawalShares: avg	19354 gas	20268 gas	-4.5096%	✅
redeemWithdrawalShares: max	57733 gas	106195 gas	-45.6349%	✅
removeLiquidity: min	1639 gas	1639 gas	0%	🟰
removeLiquidity: avg	147129 gas	149263 gas	-1.4297%	✅
removeLiquidity: max	323845 gas	323845 gas	0%	🟰

This comment was automatically generated by workflow using github-action-benchmark.

[coveralls]

coverage: 95.216%. remained the same
when pulling 110f17a on test-fix
into 846b944 on main.