find-sidebar: don't discard matches without text area
It may happen that a text match has no corresponding text area available,
(due to limitations/bugs of Poppler's TextPage->getSelectionWords()
function used by poppler-glib poppler_page_get_text_layout_for_area()
function) so in that case, instead of discarding the match, we can
just show the matched text in the sidebar without surrounding text,
because the text area is only needed to retrieve surrounding text.
Closes #1943 (closed)