This simplifies the code as it removes the need to modify and then reset
the `done` and `queue` properties.

Combines the empty() and true checks into a if/elseif structure.

For a tiny micro-optimization, wraps these checks within a not
equal to `false`.

Why?

When using the default (i.e. on the front-end and with classic themes):

* Skips running `empty()`.
* Skips reassigning `false` to `$handle`.

These skips gain a tiny tiny performance boost.

Printing `$handles` does not work (for some reason that needs to be investigated further). Overwriting
the queue and done properties does print and has been working since 6.2 alpha. This commit restores
the overwriting properties approach.