fixes #6472 / BZ 1113230 - content view filter - fix issue where filter not available

On the content view filter edit screens, it was possible for a
"really fast" user to click links that utilized the filter, before
it had actually been loaded.  Eg. Open a filter and click the 'Add' tab.

This small change will ensure that we do not render the content of the
filter edit, before the filter is actually available.
Is there a case where `filter.id` will never be defined?  If so should we show something else when it's not or while it's loading?