Merge pull request #51 from maticnetwork/dev-audit-fixes

accounts/scwallet/hub.go

accounts/scwallet/securechannel.go

accounts/scwallet/wallet.go

accounts/usbwallet/hub.go

accounts/usbwallet/trezor.go

accounts/usbwallet/wallet.go

consensus/bor/bor.go

consensus/bor/bor_test/helper.go

consensus/bor/bor_test/snapshot_test.go

consensus/bor/errors.go

consensus/bor/snapshot.go

consensus/bor/validator.go

consensus/bor/validator_set.go

consensus/clique/clique.go

consensus/clique/snapshot.go

consensus/ethash/ethash.go

core/headerchain.go

core/rawdb/freezer_table.go

core/state/database.go

graphql/service.go