Also handle terminated message when trying to add a watcher during the stopping process.
Also handle terminated message when trying to add a watcher during the stopping process.

tomliversidge/protoactor-dotnet,AsynkronIT/protoactor-dotnet,raskolnikoov/protoactor-dotnet,raskolnikoov/protoactor-dotnet,tomliversidge/protoactor-dotnet,Bee-Htcpcp/protoactor-dotnet,Bee-Htcpcp/protoactor-dotnet,masteryee/protoactor-dotnet,masteryee/protoactor-dotnet