fix: Make MulDecTruncate() return nil DecCoins when multiplier is 0

[evancholmberg]

Description

The DecCoins.MulDecTruncate function is supposed to panic instead of returning nil when multiplier d is zero. This fixes that behavior and updates the related test decCoinTestSuite.TestDecCoins_MulDecTruncate to expect a panic when multiplier d is zero.

Closes: #9790

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[tac0turtle]

LGTM, possibly in the future we can avoid panics

[atheeshp]

There are few failing tests.

[alexanderbez]

Should this be backported?

[amaury1093]

Hey @evancholmberg, simulations are failing on this PR, could you have a look?

I tried running the exact command in the failing CI: go test ./simapp -run TestAppImportExport -Enabled=true -NumBlocks=50 -Genesis= -Verbose=true -Commit=true -Seed=1 -Period=5 -ExportParamsPath /tmp/sim-logs-826299046/sim_params-1.json -ExportStatePath /tmp/sim-logs-826299046/sim_state-1.json -v -timeout 24h, and i got:

panic: invalid zero decimal

[evancholmberg]

Yes, I have time tomorrow to work on this.

[ValarDragon]

Agreed this follows the comment, confused why we want to panic vs just return sdk.DecCoins{} when the multiplier is 0.

[evancholmberg]

I can change it to return sdk.DecCoins{}. That would make sense to only have division by 0 panic i.e. in DecCoins.QuoDec() and DecCoins.QuoDecTruncate().

[ValarDragon]

I'd prefer that personally! Makes a lot more sense imo

[alexanderbez]

🌮

[atheeshp]

@evancholmberg can you resolve the conflicts here.