fix: fixed nested values in 'fields' query parameter

[sibuk-harabudjasim]

This fix solves problem when using "fields" query parameter and trying to fetch fields 2 levels deeper than target path.
For example in model:

module m {
	prefix "";
	namespace "";
	revision 0;
	container aaa {
		list bbb {
			leaf ccc {
				type string;
			}
		}
	}
	container ddd {
		leaf eee {
			type string;
		}
	}
}

request /restconf/data/m:aaa?fields=bbb/ccc will crash with panic "illegal call : base was not found to be any parent of candidate" because "fields" segments length is bigger than current candidate and this case was not covered in code.

[dhubler]

love all the commits! want to give them the time they deserve for review, but shouldn't be an issue

[sibuk-harabudjasim]

No worries, I've switched to forked version for my needs.