fix nodes panic during synchronization #544

Job	Run time
Basic Checks	1m 42s
Unit Tests	7m 48s
Integration Tests (raft)	11m 10s
Integration Tests (pvtdata)	10m 54s
Integration Tests (pvtdatapurge e2e)	10m 7s
Integration Tests (ledger)	12m 38s
Integration Tests (lifecycle)	5m 1s
Integration Tests (smartbft)	19m 20s
Integration Tests (discovery gossip devmode pluggable)	5m 27s
Integration Tests (gateway idemix pkcs11 configtx configtxlator)	16m 53s
Integration Tests (sbe nwo msp)	6m 46s
	1h 47m 46s

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