Fixed whitespace problems
Allow the container to be empty when document is loaded

This allows for Nested to be initialized on an empty container, or
a container with no boxes with predefined sizes, without throwing
an error.  This is a modified version of an [existing patch][patch]
that fixed the issue but could not be applied against Nested 1.0.3.

[patch]: https://github.com/suprb/Nested/pull/12