[3.4] fix(defrag): handle errors during defrag #15547

Job	Run time
test (linux-amd64-fmt)	59s
test (linux-amd64-integration-1-cpu)	9m 28s
test (linux-amd64-integration-2-cpu)	9m 38s
test (linux-amd64-integration-4-cpu)	10m 1s
test (linux-amd64-functional)	8m 20s
test (linux-amd64-unit-4-cpu-race)	53s
test (all-build)	3m 27s
test (linux-amd64-grpcproxy)	15m 17s
test (linux-amd64-e2e)	14m 28s
test (linux-386-unit)	36s
	1h 13m 7s

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