git-gui: Correctly cleanup msgfmt '1 message untranslated' output

git-gui: Correctly cleanup msgfmt '1 message untranslated' output

In the multiple message case we remove the word "messages" from the
statistics output of msgfmt as it looks cleaner on the tty when you
are watching the build process.  However we failed to strip the word
"message" when only 1 message was found to be untranslated or fuzzy,
as msgfmt does not produce the 's' suffix.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>