preview tabs: Fix tab selection getting out of sync (#10478)

There was an edge case where the project panel selection would not be
updated when opening a lot of tabs quickly using the preview tab
feature.
I spent way too long debugging this, thankfully @ConradIrwin spotted it
in like 5 minutes 🎉

Release Notes:

- N/A

crates/workspace/src/pane.rs

@@ -818,11 +818,10 @@ impl Pane {
                 if let Some(prev_item) = self.items.get(prev_active_item_ix) {
                     prev_item.deactivated(cx);
                 }
-
+            }
             cx.emit(Event::ActivateItem {
                 local: activate_pane,
             });
-            }
 
             if let Some(newly_active_item) = self.items.get(index) {
                 self.activation_history