chore(core-database): blocksInCurrentRound and forgingDelegates are arrays

[sebastijankuzner]

Summary

This PR set blocksInCurrentRound and forgingDelegates as array and remove possible undefined value. This fixes runtime errors when setting length value to undefined array.

Checklist

• Ready to be merged

[codecov]

Codecov Report

Merging #3902 into develop will increase coverage by 82.13%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##           develop    #3902       +/-   ##
============================================
+ Coverage    13.68%   95.81%   +82.13%     
============================================
  Files          628      628               
  Lines        14528    14526        -2     
  Branches      1728     1727        -1     
============================================
+ Hits          1988    13918    +11930     
+ Misses       12425      419    -12006     
- Partials       115      189       +74     

Flag	Coverage Δ
#functional	?
#integration	9.83% <0.00%> (+<0.01%)	⬆️
#unit	95.75% <100.00%> (?)

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Impacted Files	Coverage Δ
packages/core-database/src/database-service.ts	97.22% <100.00%> (+97.22%)	⬆️
...rc/migrations/20190307000000-drop-wallets-table.ts	0.00% <0.00%> (-100.00%)	⬇️
...c/migrations/20180305200000-create-rounds-table.ts	0.00% <0.00%> (-100.00%)	⬇️
...c/migrations/20180305300000-create-blocks-table.ts	0.00% <0.00%> (-100.00%)	⬇️
.../migrations/20180305100000-create-wallets-table.ts	0.00% <0.00%> (-100.00%)	⬇️
...igrations/20190626000000-enforce-chained-blocks.ts	0.00% <0.00%> (-100.00%)	⬇️
...rations/20191003000000-migrate-vendor-field-hex.ts	0.00% <0.00%> (-100.00%)	⬇️
...ations/20180305400000-create-transactions-table.ts	0.00% <0.00%> (-100.00%)	⬇️
.../20190718000000-check_previous_block-add-schema.ts	0.00% <0.00%> (-100.00%)	⬇️
...20190619000000-drop-id-column-from-rounds-table.ts	0.00% <0.00%> (-100.00%)	⬇️
... and 587 more

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