To check if dictionary is missing we have to run spelling which
checks used language for each text portion.
When AutoSpelling or manually invoked Spelling is performed SwDoc
receives notification about missing dictionaries. Then it is possible
to not show 'Completed' dialog.

Change-Id: I040ce6565632294796c0206d20c4cd0066ca9643
Reviewed-on: https://gerrit.libreoffice.org/66813
Tested-by: Jenkins
Reviewed-by: Szymon Kłos <szymon.klos@collabora.com>