lib/vsprintf.c: fix interaction of kasprintf() and vsnprintf() when using %pV

Otherwise, the warning at the top of vsnprintf() gets triggered by
kvasprintf()'s first invocation (with NULL buffer and zero size) of
vsnprintf().

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/vsprintf.c

@@ -898,7 +898,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 	case 'U':
 		return uuid_string(buf, end, ptr, spec, fmt);
 	case 'V':
-		return buf + vsnprintf(buf, end - buf,
+		return buf + vsnprintf(buf, end > buf ? end - buf : 0,
 				       ((struct va_format *)ptr)->fmt,
 				       *(((struct va_format *)ptr)->va));
 	case 'K':