Restarting miners doesn't reinitialize state

[K-Kumar-01]

Fixes #1755

Changes

• check for the current round number or lfb
• initialize only when the round is zero or LFB is nil

Need to be mentioned in CHANGELOG.md?

Details about state can be mentioned.

Tests

Tasks to complete before merging PR:

• Ensure system tests are passing. If not Run them manually to check for any regressions 📋
• Do any new system tests need added to test this change? do any existing system tests need updated? If so create a PR at 0chain/system_test
• Merge your system tests PR to master AFTER merging this PR

[codecov-commenter]

Codecov Report

Merging #1875 (73686bd) into staging (3a37926) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           staging    #1875      +/-   ##
===========================================
- Coverage    26.87%   26.86%   -0.02%     
===========================================
  Files          356      356              
  Lines        59206    59195      -11     
===========================================
- Hits         15912    15902      -10     
- Misses       41389    41392       +3     
+ Partials      1905     1901       -4     

Flag	Coverage Δ
Unit-Tests	26.86% <ø> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
code/go/0chain.net/miner/protocol_round.go	5.15% <ø> (ø)
...de/go/0chain.net/smartcontract/vestingsc/config.go	50.52% <0.00%> (-4.74%)	⬇️
code/go/0chain.net/core/datastore/worker.go	97.26% <0.00%> (-2.74%)	⬇️
...ain.net/smartcontract/storagesc/benchmark_tests.go	76.54% <0.00%> (ø)
...ain.net/smartcontract/storagesc/config_settigns.go	54.76% <0.00%> (ø)
...e/go/0chain.net/smartcontract/dbs/event/process.go	1.89% <0.00%> (+<0.01%)	⬆️
...ain.net/smartcontract/storagesc/benchmark_setup.go	4.41% <0.00%> (+0.19%)	⬆️

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[peterlimg]

LGTM