fix: a panic in one session's I/O ends that session cleanly

Every client's reader thread (Telnet/RAW, serial, local shell, IRC, VNC,
RDP) and SSH's channel reader task now run under clients::guarded /
guarded_task. A panic there, such as a decoder bug triggered by a
hostile server, reports 'internal error: …' through the session's
on_error and then closes it, so the tab shows the error (and
auto-reconnect can run) instead of looking connected with nothing
reading. Other sessions were already unaffected since the switch to
parking_lot locks.

rust/core/src/clients/serial.rs

@@ -90,7 +90,7 @@ impl SerialClient {
             *guard = Some((port, stop.clone()));
         }
         let me = inner.clone();
-        std::thread::spawn(move || me.read_loop(reader, stop));
+        std::thread::spawn(super::guarded(inner.cb.on_error.clone(), inner.cb.on_close.clone(), move || me.read_loop(reader, stop)));
         Ok(())
     }