Switching now handles callbacks correctly.

src/switch.zig

@@ -70,6 +70,7 @@ pub const SwitchDB = struct {
         var managedconnection = self.db.get(fd) orelse return error.unregisteredFD;
         managedconnection.in = in;
         managedconnection.out = out;
+        try self.db.put(fd, managedconnection);
     }
 
     /// Dig the "db" hashmap, perform "in" fn, may provide a message.