actually, initialize the whole memory block to zero

While allocating the object, we might as well initialize the whole memory block to zero in order to protect against hidden issues.

ext/nio4r/monitor.c

@@ -64,7 +64,7 @@ static VALUE NIO_Monitor_allocate(VALUE klass)
     if(!monitor)
         return Qnil;
 
-    monitor->self = Qnil;
+    *monitor = (struct NIO_Monitor){.self = Qnil};
     return Data_Wrap_Struct(klass, NIO_Monitor_mark, NIO_Monitor_free, monitor);
 }