Bug#996647: xdg-email with KDE and Thunderbird

[Шлыков Василий]

I believe this bug due to bug in open_kde function in xdg-email file.
kreadconfig5 reports that configured "thunderbird.desktop" tool. 
Obviously this is not a executable file.

This cound be fixed by adding one line to xdg-email:

            if echo "$client" | grep -Eq 'thunderbird|icedove'; then
this line >     client=`desktop_file_to_binary "$client"`
                run_thunderbird "$client" "$1"
            fi

Best regards
Vasiliy Shlykov