Fixed a side-effect of 03519c14b06f86880259b21d3ba07f646606e828 from
@matabele whereby the current tiddler is overwritten by the
`<$tiddler>` widget, which means that it is not accessible when
rendering the caption of the tab.
This causes a problem with eg the “Add Plugins” modal where it breaks
the count on the tabs.
0747635fba