mux: client would prune out the empty window when connecting via ssh/tls domain

When the client connected to an empty remote mux, it would allocate an
empty window and then spawn a new tab into it.

Meanwhile, the authentication window would close and trigger a prune of
all empty windows, causing the in-flight spawn to fail because its
destination window was removed.

This commit defers window pruning while Activity is in progress;
the MuxWindowBuilder has an associated Activity count.

mux/src/lib.rs

@@ -426,6 +426,9 @@ impl Mux {
     }
 
     pub fn prune_dead_windows(&self) {
+        if Activity::count() > 0 {
+            return;
+        }
         let live_tab_ids: Vec<TabId> = self.tabs.borrow().keys().cloned().collect();
         let mut dead_windows = vec![];
         let dead_tab_ids: Vec<TabId>;

wezterm-gui/src/main.rs

@@ -269,8 +269,7 @@ async fn spawn_tab_in_default_domain_if_mux_is_empty(
 
     let config = config::configuration();
     let window_id = mux.new_empty_window();
-    let _tab = mux
-        .default_domain()
+    let _tab = domain
         .spawn(config.initial_size(), cmd, None, *window_id)
         .await?;
     Ok(())