fix nil issues reported by nilness and staticcheck

[gzliudan]

Proposed changes

This PR fixes the nil issues reported by from nilness and staticcheck.

• issues from staticcheck

cmd/puppeth/wizard_netstats.go:85:20: possible nil pointer dereference (SA5011)
        cmd/puppeth/wizard_netstats.go:88:5: this check suggests that the pointer can be nil
mobile/ethereum.go:71:24: possible nil pointer dereference (SA5011)
        mobile/ethereum.go:68:5: this check suggests that the pointer can be nil

• issues from nilness

consensus/XDPoS/engines/engine_v2/forensics.go:212:125: nil dereference in field selection

light/postprocess.go:167:8: panic with nil value
les/backend.go:150:8: panic with nil value
les/odr_requests.go:199:8: panic with nil value
les/odr_requests.go:359:8: panic with nil value
les/peer.go:282:8: panic with nil value
les/peer.go:304:8: panic with nil value
les/peer.go:323:8: panic with nil value
les/randselect.go:112:9: panic with nil value
les/randselect.go:172:7: panic with nil value
les/retrieve.go:309:8: panic with nil value
p2p/discv5/ticket.go:444:8: panic with nil value
p2p/discv5/ticket.go:805:7: panic with nil value

accounts/abi/bind/base.go:294:9: impossible condition: nil != nil
whisper/whisperv6/whisper.go:504:9: impossible condition: nil != nil

consensus/clique/clique.go:393:11: tautological condition: nil == nil
trie/trie.go:244:11: tautological condition: nil == nil

consensus/XDPoS/engines/engine_v1/engine.go:479:11: tautological condition: nil == nil
cmd/gc/main.go:190:17: tautological condition: non-nil != nil
cmd/gc/main.go:173:19: tautological condition: non-nil != nil
core/blockchain.go:1665:46: tautological condition: non-nil != nil
core/blockchain.go:1944:45: tautological condition: non-nil != nil
core/order_pool_test.go:64:9: impossible condition: nil != nil
eth/handler.go:286:10: tautological condition: non-nil != nil

Types of changes

What types of changes does your code introduce to XDC network?
Put an ✅ in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)
• Regular KTLO or any of the maintaince work. e.g code style
• CICD Improvement

Impacted Components

Which part of the codebase this PR will touch base on,

Put an ✅ in the boxes that apply

• Consensus
• Account
• Network
• Geth
• Smart Contract
• External components
• Not sure (Please specify below)

Checklist

Put an ✅ in the boxes once you have confirmed below actions (or provide reasons on not doing so) that

• This PR has sufficient test coverage (unit/integration test) OR I have provided reason in the PR description for not having test coverage
• Provide an end-to-end test plan in the PR description on how to manually test it on the devnet/testnet.
• Tested the backwards compatibility.
• Tested with XDC nodes running this version co-exist with those running the previous version.
• Relevant documentation has been updated as part of this PR
• N/A