blockstore: Allow fallback for AddressSignature index() #4862

Job	Run time
cargo-test-sbf (token/program)	7m 33s
check	0s
cargo-test-sbf (instruction-padding/program, token/program-2022, token/program-2022-test)	13m 24s
test	0s
cargo-test-sbf (associated-token-account/program, associated-token-account/program-test)	10m 38s
cargo-test-sbf (token-upgrade/program)	8m 30s
cargo-test-sbf (feature-proposal/program)	9m 26s
cargo-test-sbf (governance/addin-mock/program, governance/program)	13m 17s
cargo-test-sbf (memo/program)	7m 21s
cargo-test-sbf (name-service/program)	8m 10s
cargo-test-sbf (stake-pool/program)	12m 23s
cargo-test-sbf (single-pool/program)	9m 16s
	1h 39m 58s

Provide feedback