compat/hstrerror: convert sprintf to snprintf
compat/hstrerror: convert sprintf to snprintf

This is a trivially correct use of sprintf, as our error
number should not be excessively long. But it's still nice
to drop an sprintf call.

Note that we cannot use xsnprintf here, because this is
compat code which does not load git-compat-util.h.

Signed-off-by: Jeff King <696e3fbcf235d40b6ea1ebd61c87cbea79d444e7@peff.net>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git