Root node fails as an array

[satkunas]

Assume the following data:

{
    "test": 12.34
}

compiling with $.test works.

However, when the root node is an array:

[{
    "test": 12.34
}]

compiling with either $[0].test or $[:].test fails

[oliveagle]

merged. and there are two cases needs to be fixed.

		case "idx":
			if len(s.key) > 0 {
				// no key `$[0].test`
				obj, err = get_key(obj, s.key)
				if err != nil {
					return nil, err
				}
			}

		case "range":
			if len(s.key) > 0 {
				// no key `$[:1].test`
				obj, err = get_key(obj, s.key)
				if err != nil {
					return nil, err
				}
			}

I fixed case range branch.