emacs: notmuch-hello: Don't include extra spaces in widget values.

emacs: notmuch-hello: Don't include extra spaces in widget values.

Previously, trailing spaces after each saved-search name were included
as part of the widget. This is going to be problematic for a future
change that will extract the widget's value and compare it to the
configured names of saved searches.

Instead, just include the name itself in the widget, and then insert
the spaces for separation afterwards.