`sess` targets a dead connection after reload if session watcher turns from on to off

[Fred-Wu]

If session watcher turns from on to off, and VS Code is reloaded, the existing R process would retain the previously installed sess hooks. Those can target the dead connection, breaking viewers such as

> plot(1:10)
warning messages from top-level task callback 'sess.workspace'
Warning message:
In value[[3L]](cond) :
  [sess] Failed to send IPC message: Native call to `processx_connection_write_bytes` failed
> View(dat)
Warning message:
In value[[3L]](cond) :
  [sess] Failed to send IPC message: Native call to `processx_connection_write_bytes` failed
warning messages from top-level task callback 'sess.workspace'
Warning message:
In value[[3L]](cond) :
  [sess] Failed to send IPC message: Native call to `processx_connection_write_bytes` failed
> help(glm)
Warning message:
In value[[3L]](cond) :
  [sess] Failed to send IPC message: Native call to `processx_connection_write_bytes` failed
warning messages from top-level task callback 'sess.workspace'
Warning message:
In value[[3L]](cond) :
  [sess] Failed to send IPC message: Native call to `processx_connection_write_bytes` failed