copernet/copernicus: logic/lmempool/ltxmempool.go; 5 LoC

Found a possible issue in [copernet/copernicus](https://www.github.com/copernet/copernicus) at [logic/lmempool/ltxmempool.go](https://github.com/copernet/copernicus/blob/46353c3fb80dbfb0da4546a79351ef2d84ed809d/logic/lmempool/ltxmempool.go#L217-L221)

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.

> function call at line 218 passes reference to preout to third-party code

[Click here to see the code in its original context.](https://github.com/copernet/copernicus/blob/46353c3fb80dbfb0da4546a79351ef2d84ed809d/logic/lmempool/ltxmempool.go#L217-L221)

Click here to show the 5 line(s) of Go which triggered the analyzer.

```go
for _, preout := range trax.GetAllPreviousOut() {
if coinsMap.FetchCoin(&preout) == nil {
return false
}
}

```

Click here to show extra information the analyzer produced.

```
No path was found through the callgraph that could lead to a function which writes a pointer argument.

The following graphviz dot graph describes paths through the callgraph that could lead to a function which passes a pointer to third-party code:
digraph G {
"(FetchCoin, 1)" -> {}
}

```

Leave a reaction on this issue to contribute to the project by classifying this instance as a **Bug** :-1:, **Mitigated** :+1:, or **Desirable Behavior** :rocket:
See the descriptions of the classifications [here](https://github.com/github-vet/rangeclosure-findings#how-can-i-help) for more information.

commit ID: 46353c3fb80dbfb0da4546a79351ef2d84ed809d

Start at logic/lmempool/ltxmempool.go lines 217-221 and inspect FetchCoin's signature and implementation. Review the analyzer finding about passing &preout, then determine whether the behavior is a bug, mitigated, or desirable and leave the corresponding classification reaction.

Written by the indexing model from the issue text.