… any more

In MSVC2015 the behavior of vsnprintf was changed.
W/o this fix there is one character missing at the end.

Signed-off-by: Sven Strickroth <sven@cs-ware.de>
Acked-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Acked-by: Sebastian Schuberth <sschuberth@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>