QBFT: fix chain fork when emptyblockperiodseconds is enabled #1101

Job	Run time
Code linters	4m 18s
Build Docker image	2m 30s
Unit tests in ubuntu-20.04	27m 33s
Run PEEPS tests	14m 47s
Acceptance tests (basic \|\| basic-raft \|\| (advanced && raft) \|\| networks/typical::raft)	20m 32s
Acceptance tests (basic \|\| basic-istanbul \|\| (advanced && istanbul && !block-heights) \|\| networks/typical::istanbul)	23m 6s
Acceptance tests (basic \|\| basic-istanbul \|\| (advanced && istanbul && !block-heights) \|\| empty-block-period \|\| block-reward \|\| networks/typical::qbft)	22m 14s
Acceptance tests (validator-management && networks/template::istanbul-3plus1)	8m 49s
Acceptance tests (validator-management && networks/template::qbft-3plus1)	8m 51s
Acceptance tests (multitenancy && networks/plugins::raft-multitenancy)	38s
Acceptance tests (migration && networks/template::istanbul-4nodes)	6m 2s
Acceptance tests (migration && networks/template::raft-4nodes)	5m 10s
Acceptance tests (basic \|\| networks/typical::raftmps)	16m 52s
Acceptance tests (basic \|\| networks/typical::istanbulmps)	22m 22s
Acceptance tests (basic \|\| networks/typical::qbftmps)	22m 23s
	3h 26m 7s

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