fix: check CountSubKeys nil (#15059)

## Description

Closes:
#6889
#15056



---

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CHANGELOG.md

@@ -271,6 +271,7 @@ extension interfaces. `module.Manager.Modules` is now of type `map[string]interf
 
 ### Bug Fixes
 
+* (x/auth) [#15059](https://github.com/cosmos/cosmos-sdk/pull/15059) `ante.CountSubKeys` returns 0 when passing a nil `Pubkey`.
 * (x/capability) [#15030](https://github.com/cosmos/cosmos-sdk/pull/15030) Fixed bug where `x/capability` consumed `GasMeter` gas during `InitMemStore`.
 * [#14995](https://github.com/cosmos/cosmos-sdk/pull/14995) Allow unknown fields in `ParseTypedEvent`.
 * [#14952](https://github.com/cosmos/cosmos-sdk/pull/14952) Pin version of github.com/syndtr/goleveldb `v1.0.1-0.20210819022825-2ae1ddf74ef7` to avoid issues in the store.

x/auth/ante/ante_test.go

@@ -1307,6 +1307,7 @@ func TestCountSubkeys(t *testing.T) {
 		{"single key", args{singleKey}, 1},
 		{"single level multikey", args{singleLevelMultiKey}, 5},
 		{"multi level multikey", args{multiLevelMultiKey}, 11},
+		{"nil key", args{nil}, 0},
 	}
 	for _, tc := range testCases {
 		t.Run(tc.name, func(T *testing.T) {

x/auth/ante/sigverify.go

@@ -461,7 +461,12 @@ func GetSignerAcc(ctx sdk.Context, ak AccountKeeper, addr sdk.AccAddress) (sdk.A
 }
 
 // CountSubKeys counts the total number of keys for a multi-sig public key.
+// A non-multisig, i.e. a regular signature, it naturally a count of 1. If it is a multisig,
+// then it recursively calls it on its pubkeys.
 func CountSubKeys(pub cryptotypes.PubKey) int {
+	if pub == nil {
+		return 0
+	}
 	v, ok := pub.(*kmultisig.LegacyAminoPubKey)
 	if !ok {
 		return 1