Random Fuzzer panic: invalid argument to Intn

[npinto]

Summary of Bug

go test ./cmd/gaia/app -run TestFullGaiaSimulation -SimulationEnabled=true -SimulationNumBlocks=500 -SimulationGenesis= -SimulationVerbose=true -SimulationCommit=true -SimulationSeed=7601778 -SimulationPeriod=50 -v -timeout 24h

fails with the following error message:

--- FAIL: TestFullGaiaSimulation (0.11s)
panic: invalid argument to Intn [recovered]
        panic: invalid argument to Intn

goroutine 26 [running]:
testing.tRunner.func1(0xc0004b3e00)
        /snap/go/3739/src/testing/testing.go:830 +0x392
panic(0xe5c820, 0x1295c00)
        /snap/go/3739/src/runtime/panic.go:522 +0x1b5
math/rand.(*Rand).Intn(0xc0000f8ff0, 0x0, 0xc0004b0b40)
        /snap/go/3739/src/math/rand/rand.go:169 +0x9c
github.com/cosmos/cosmos-sdk/x/simulation.GetMemberOfInitialState(0xc0000f8ff0, 0xc00003d720, 0x3, 0x3, 0x1)
        /home/cosmos/go/src/github.com/cosmos/cosmos-sdk/x/simulation/transition_matrix.go:61 +0x57
github.com/cosmos/cosmos-sdk/x/simulation.newMockValidators(0xc0000f8ff0, 0xc001240000, 0x11, 0x24, 0x3fe8ce8eddf631bd, 0xc4, 0x3fef72b3d35c098b, 0xc00003d720, 0x3, 0x3, ...)
        /home/cosmos/go/src/github.com/cosmos/cosmos-sdk/x/simulation/mock_tendermint.go:37 +0x168
github.com/cosmos/cosmos-sdk/x/simulation.initChain(0xc0000f8ff0, 0x3fe8ce8eddf631bd, 0xc4, 0x3fef72b3d35c098b, 0xc00003d720, 0x3, 0x3, 0xc0000eab90, 0x3, 0x3, ...)
        /home/cosmos/go/src/github.com/cosmos/cosmos-sdk/x/simulation/simulate.go:47 +0x1e8
github.com/cosmos/cosmos-sdk/x/simulation.SimulateFromSeed(0x12dac80, 0xc0004b3e00, 0x12accc0, 0xc0000c2008, 0xc0000ee7e0, 0x1153ba8, 0x73fe72, 0xc00007fc20, 0xf, 0xf, ...)
        /home/cosmos/go/src/github.com/cosmos/cosmos-sdk/x/simulation/simulate.go:80 +0x604
github.com/cosmos/cosmos-sdk/cmd/gaia/app.TestFullGaiaSimulation(0xc0004b3e00)
        /home/cosmos/go/src/github.com/cosmos/cosmos-sdk/cmd/gaia/app/sim_test.go:376 +0x375
testing.tRunner(0xc0004b3e00, 0x1153b68)
        /snap/go/3739/src/testing/testing.go:865 +0xc0
created by testing.(*T).Run
        /snap/go/3739/src/testing/testing.go:916 +0x35a
FAIL    github.com/cosmos/cosmos-sdk/cmd/gaia/app       0.234s

Version

$ gaiad version --long
gaia: 0.34.3-128-g3153e934
git commit: 3153e93446ad5cda029b96c408c2bbfb1b91adc1
build tags: netgo,ledger
go version go1.12.5 linux/amd64

$ gaiacli version --long
gaia: 0.34.3-128-g3153e934
git commit: 3153e93446ad5cda029b96c408c2bbfb1b91adc1
build tags: netgo,ledger
go version go1.12.5 linux/amd64

Steps to Reproduce

go test ./cmd/gaia/app -run TestFullGaiaSimulation -SimulationEnabled=true -SimulationNumBlocks=500 -SimulationGenesis= -SimulationVerbose=true -SimulationCommit=true -SimulationSeed=7601778 -SimulationPeriod=50 -v -timeout 24h

---

For Admin Use

• Not duplicate issue
• Appropriate labels applied
• Appropriate contributors tagged
• Contributor assigned/self-assigned

[rigelrozanski]

Thanks for submitting this bug - I'll tryn' fix right away