fix: check length of minimega response slice before accessing

There are times when the `disk info` command does not return a valid
response and the response length was not checked before trying to access
it.

src/go/util/mm/minimega.go

@@ -218,14 +218,19 @@ func (this Minimega) GetVMInfo(opts ...Option) VMs {
  cmd.Command = fmt.Sprintf("mesh send %s %s", row["host"], cmd.Command)
  }
 
- // Only expect one row returned
- // TODO (btr): check length to avoid a panic.
- resp := mmcli.RunTabular(cmd)[0]
+ resp := mmcli.RunTabular(cmd)
 
- if resp["backingfile"] == "" {
- vm.Disk = resp["image"]
+ if len(resp) == 0 {
+ vm.Disk = disk
  } else {
- vm.Disk = resp["backingfile"]
+ // Only expect one row returned
+ info := resp[0]
+
+ if info["backingfile"] == "" {
+ vm.Disk = info["image"]
+ } else {
+ vm.Disk = info["backingfile"]
+ }
  }
  } else {
  // Attempting to get disk info when not using a snapshot will cause a