snprintf() should always return non-negative result. According to

Microsoft documentation about _vscprintf():

  If format is a null pointer, the invalid parameter handler is invoked,
  as described in Parameter Validation. If execution is allowed to
  continue, the functions return -1 and set errno to EINVAL.

The UNIX variant of snprintf() segfaults if format is a NULL pointer
(similar to strlen(NULL) for example), so it is better to conform to
this behavior and crash our custom Windows version instead of
returning -1. Noone would expect -1 to be returned from snprintf().

Cosmetic: Add a space after typecast.

Approved by:	Marko

ut/ut0ut.c

@@ -528,15 +528,12 @@ ut_snprintf(
 	va_start(ap2, fmt);
 
 	res = _vscprintf(fmt, ap1);
-
-	if (res == -1) {
-		return(-1);
-	}
+	ut_a(res != -1);
 
 	if (size > 0) {
 		_vsnprintf(str, size, fmt, ap2);
 
-		if ((size_t)res >= size) {
+		if ((size_t) res >= size) {
 			str[size - 1] = '\0';
 		}
 	}