nogvl_wait_for_single_fd must wait as its name

poll(fds, n, 0) mean no timeout and immediately return. If you want to
wait something, you need to use -1 instead.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58534 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

io.c

@@ -10370,7 +10370,7 @@ nogvl_wait_for_single_fd(int fd, short events)
     fds.fd = fd;
     fds.events = events;
 
-    return poll(&fds, 1, 0);
+    return poll(&fds, 1, -1);
 }
 
 static int