store/internal/proofs: CreateNonMembershipProof/CreateMembershipProof panic with empty key

[cuonglm]

Summary of Bug

CreateNonMembershipProof/CreateMembershipProof does not validate the key before calling sdkmaps.ProofsFromMap, so they can panic with empty key.

Version

4f4c035

Steps to Reproduce

package main

import (
	"fmt"

	"github.com/cosmos/cosmos-sdk/store/internal/proofs"
)

func main() {
	icp, err := proofs.CreateNonMembershipProof(map[string][]byte{``: nil}, []byte(` `))
	if err != nil {
		panic(err)
	}
	fmt.Println(icp)
}

package main

import (
	"fmt"

	"github.com/cosmos/cosmos-sdk/store/internal/proofs"
)

func main() {
	icp, err := proofs.CreateMembershipProof(map[string][]byte{``: nil}, []byte(``))
	if err != nil {
		panic(err)
	}
	fmt.Println(icp)
}

Discover by https://oss-fuzz.com/testcase-detail/4647668077953024

---

For Admin Use

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

[cuonglm]

cc @odeke-em