Log Message:
poppler: update to 21.06.1

Release 21.06.1:
        glib:
         * fix poppler_rectangle_free() regression. Issue #1087

Release 21.06.0:
        core:
         * Fix rendering of some extended latin1 characters in annotations. \ 
Issue #1070
         * Support some not so well formed documents with password. Issue #1083
         * Add API to get notified if the xref is reconstructed
         * Add somewhat fancier left/right signature visual representation
         * Fix crashes in malformed files
         * Minor code improvements

        qt6:
         * Change some functions to return std::unique_ptr

        qt5/qt6:
         * Add API to get notified if the xref is reconstructed
         * Add somewhat fancier left/right signature visual representation
         * Don't assert when trying to invert singular matrices

        build system:
         * make boost opt-out if building splash