zhengq1/go-vm: vm/common.go; 22 LoC

Found a possible issue in [zhengq1/go-vm](https://www.github.com/zhengq1/go-vm) at [vm/common.go](https://github.com/zhengq1/go-vm/blob/a74e3575dfcbf50ebfc321f39e2d4ceb0e864743/vm/common.go#L104-L125)

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.

> reference to b is reassigned at line 121

[Click here to see the code in its original context.](https://github.com/zhengq1/go-vm/blob/a74e3575dfcbf50ebfc321f39e2d4ceb0e864743/vm/common.go#L104-L125)

Click here to show the 22 line(s) of Go which triggered the analyzer.

```go
for _, b := range bigints {
var nb *big.Int

switch op{
case OP_1ADD:
nb = b.Add(&b, big.NewInt(int64(1)))
case OP_1SUB:
nb = b.Sub(&b, big.NewInt(int64(1)))
case OP_2MUL:
nb = b.Lsh(&b, 2)
case OP_2DIV:
nb = b.Rsh(&b, 2)
case OP_NEGATE:
nb = b.Neg(&b)
case OP_ABS:
nb = b.Abs(&b)
default:
nb = &b

}
newbigints = append(newbigints, *nb)
}

```

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: a74e3575dfcbf50ebfc321f39e2d4ceb0e864743