Kind of fix translations

Lots of untranslated strings remain

https://bugzilla.gnome.org/show_bug.cgi?id=703805
check for none in set_value

This fixes undo when only one number is on the board.

https://bugzilla.gnome.org/show_bug.cgi?id=731011
Fix exception when starting new game

https://bugzilla.gnome.org/show_bug.cgi?id=703335
Prepare 3.8.2