fix(telemetry): fix crash due to telemetry

[NamanJain8]

We are seeing a crash in zero. This PR fixes this.

panic: runtime error: integer divide by zero
goroutine 194 [running]:
github.com/dgraph-io/dgraph/worker.(*groupi).connToZeroLeader(0x31c07a0, 0x205af60)
	/home/ash/go/src/github.com/dgraph-io/dgraph-release/worker/groups.go:681 +0x452
github.com/dgraph-io/dgraph/worker.(*groupi).askZeroForEE.func1(0xc000136000)
	/home/ash/go/src/github.com/dgraph-io/dgraph-release/worker/groups.go:1100 +0x75
github.com/dgraph-io/dgraph/worker.(*groupi).askZeroForEE(0x31c07a0, 0xc0000e6000)
	/home/ash/go/src/github.com/dgraph-io/dgraph-release/worker/groups.go:1123 +0xa9
github.com/dgraph-io/dgraph/worker.EnterpriseEnabled(0x12e)
	/home/ash/go/src/github.com/dgraph-io/dgraph-release/worker/groups.go:1090 +0x63
github.com/dgraph-io/dgraph/worker.GetEEFeaturesList(0xc00013c230, 0x12e, 0x1a1)
	/home/ash/go/src/github.com/dgraph-io/dgraph-release/worker/groups.go:1061 +0x26
github.com/dgraph-io/dgraph/telemetry.(*Telemetry).Post(0xc00077c5a0, 0x0, 0x0)
	/home/ash/go/src/github.com/dgraph-io/dgraph-release/telemetry/telemetry.go:92 +0x52
github.com/dgraph-io/dgraph/dgraph/cmd/zero.(*Server).periodicallyPostTelemetry(0xc0000f0c80)
	/home/ash/go/src/github.com/dgraph-io/dgraph-release/dgraph/cmd/zero/zero.go:130 +0x2b9
created by github.com/dgraph-io/dgraph/dgraph/cmd/zero.run

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This change is