Guard against no attesters within committee in VerifyAttestationNoVerifySignature (#15169)

* Guard against no attesters within committee in `VerifyAttestationNoVerifySignature`

* changelog fragment

proto/prysm/v1alpha1/attestation/attestation_utils.go

@@ -111,7 +111,7 @@ func AttestingIndices(att ethpb.Att, committees ...[]primitives.ValidatorIndex)
 
 	attesters := make([]uint64, 0, aggBits.Count())
 	committeeOffset := 0
-	for _, c := range committees {
+	for ci, c := range committees {
 		committeeAttesters := make([]uint64, 0, len(c))
 		for i, vi := range c {
 			if aggBits.BitAt(uint64(committeeOffset + i)) {
@@ -119,7 +119,7 @@ func AttestingIndices(att ethpb.Att, committees ...[]primitives.ValidatorIndex)
 			}
 		}
 		if len(committeeAttesters) == 0 {
-			return nil, fmt.Errorf("no attesting indices found in committee %v", c)
+			return nil, fmt.Errorf("no attesting indices found for committee index %d", ci)
 		}
 		attesters = append(attesters, committeeAttesters...)
 		committeeOffset += len(c)

proto/prysm/v1alpha1/attestation/attestation_utils_test.go

@@ -81,6 +81,14 @@ func TestAttestingIndices(t *testing.T) {
 			},
 			want: []uint64{0, 1},
 		},
+		{
+			name: "Electra - No attester in committee",
+			args: args{
+				att:        &eth.AttestationElectra{AggregationBits: bitfield.Bitlist{0b11100}},
+				committees: [][]primitives.ValidatorIndex{{0, 1}, {0, 1}},
+			},
+			err: "no attesting indices found for committee index 0",
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {