Bug-Fix: ABI encode infer to slice IsNil handler removal

[ahangsu]

Description

On the input of array in golang to function inferToSlice, the previous implementation will try to infer IsNil from interface value, while this will cause panic.

Solution here is to remove following code snippet

	if reflectVal.IsNil() {
		if reflectVal.Kind() == reflect.Slice {
			return nil, nil
		}
		return nil, fmt.Errorf("cannot infer nil value for array kind interface")
	}

since on passing nil slice, we still want to return an empty (len == 0) slice of interface, rather than a nil slice, which will cause trouble in implementation.

This is a fix for algorand/go-algorand-sdk#302