printf.3: Fix a small bug in example code

Move the second call to va_end(ap) to above the if-block that
precedes it, so that the va_list 'ap' will be cleaned up in
all cases.

Reported-by: Erik Roland van der Meer <ervdmeer@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man3/printf.3

@@ -1157,11 +1157,12 @@ make_message(const char *fmt, ...)
 
     va_start(ap, fmt);
     size = vsnprintf(p, size, fmt, ap);
+    va_end(ap);
+
     if (size < 0) {
         free(p);
         return NULL;
     }
-    va_end(ap);
 
     return p;
 }