Some commands are still sent to JS evaluator C++ layer even after it fails

When the new C++ layer is starting up, some JS Evaluator commands still pass through, send the command to the now exited C++ layer, and wait for a response.

Due to this, those commands leak and stay hung forever.

Note: These commands are waiting on the old C++ layer, which is already exited.

One promising approach is to use an atomic counter to keep track of goroutines that have passed through despite the C++ layer failing. Only after all those goroutines have registered on their waiters for a response from the (now defunct) C++ layer we will go ahead and unblock/fail them.

Note: The idea of "registering their waiter" is implemented as the goroutines adding an entry into the waiter map.