fix Implicit conversion loses integer precision: 'ssize_t' (aka 'long…

…') to 'int'

event.c

@@ -2573,7 +2573,7 @@ static int
 evthread_notify_base_default(struct event_base *base)
 {
 	char buf[1];
-	int r;
+    ev_ssize_t r;
 	buf[0] = (char) 0;
 #ifdef _WIN32
 	r = send(base->th_notify_fd[1], buf, 1, 0);