Cli: Short flag name don't trigger required setting

[errashe]

app.Flags = []cli.Flag{
    cli.StringSliceFlag{
      Name: "names, N",
      Required: true,
    },
  }

For example, flag setted as described, and i can write in terminal something like cli --names qwe --names asd - and that's fine. But also i should be able to write cli -N qwe -N asd and that's should work too, but i've got error.

Required flag "names" not set

[AudriusButkevicius]

A small repro would be nice, so we don't have to spend time crafting it up ourselves.

[errashe]

https://gist.github.com/errashe/2523b86554350a5e721ad015aecae796

Here we can run go run t.go --names qwe --names asd and that's will be fine. But if we try to use short tag - go run t.go -N qwe -N asd - got error (Required flag "names" not set).

[lynncyrin]

Thanks @errashe! That repro makes sense, I'm marking this as help wanted since it's a pretty obvious bug.