EDXFund/MasterChain: eth/fetcher/fetcher.go; 21 LoC

Found a possible issue in [EDXFund/MasterChain](https://www.github.com/EDXFund/MasterChain) at [eth/fetcher/fetcher.go](https://github.com/EDXFund/MasterChain/blob/6ad8bdd0f74aeedc74a3773f9e6d2a0f7b2e33b5/eth/fetcher/fetcher.go#L439-L459)

Below is the message reported by the analyzer for this snippet of code. Beware that the analyzer only reports the first
issue it finds, so please do not limit your consideration to the contents of the below message.

> range-loop variable requestHash used in defer or goroutine at line 448

[Click here to see the code in its original context.](https://github.com/EDXFund/MasterChain/blob/6ad8bdd0f74aeedc74a3773f9e6d2a0f7b2e33b5/eth/fetcher/fetcher.go#L439-L459)

Click here to show the 21 line(s) of Go which triggered the analyzer.

```go
for peer, requestHash := range request {
fmt.Println("Fetching scheduled headers", "peer", peer, "list", requestHash)

// Create a closure of the fetch and schedule in on a new thread
fetchHeader := f.fetching[requestHash[0].hash].fetchHeader
go func() {
if f.fetchingHook != nil {
hashs := []common.Hash{}
var shardId uint16
for _, rhash := range requestHash {
shardId = rhash.shardId
hashs = append(hashs, rhash.hash) // Suboptimal, but protocol doesn't allow batch header retrievals
}
f.fetchingHook(hashs, shardId)
}
for _, rhash := range requestHash {
headerFetchMeter.Mark(1)
fetchHeader(rhash.hash, rhash.shardId) // Suboptimal, but protocol doesn't allow batch header retrievals
}
}()
}

```

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commit ID: 6ad8bdd0f74aeedc74a3773f9e6d2a0f7b2e33b5