decoder panics on empty url value

[mihaiav]

The code below panics with index out of range. It seems a trivial / common use case so I wonder why it wasn't caught earlier.

        type T1 struct {
		F1 string `form:"F1"`
	
	}
	in := url.Values{
		"F1":     []string{}, 
	}

	v := new(T1)
	if err := dec.Decode(v, in); err != nil{
		panic(err)
	}

[deankarn]

Thanks for reporting @mihaiav will fix ASAP