Fix panic when opening multiple definitions in a multibuffer

The editor is on the stack, so adding an item to the `Pane` containing
the editor will cause a double borrow and a consequent panic. This
commit fixes the issue by deferring the opening of the definitions.

crates/editor/src/editor.rs

@@ -5680,6 +5680,7 @@ impl Editor {
             }
         } else if !definitions.is_empty() {
             let replica_id = self.replica_id(cx);
+            cx.window_context().defer(move |cx| {
                 let title = definitions
                     .iter()
                     .find(|definition| definition.origin.is_some())
@@ -5701,7 +5702,8 @@ impl Editor {
                     .collect();
                 workspace.update(cx, |workspace, cx| {
                     Self::open_locations_in_multibuffer(workspace, locations, replica_id, title, cx)
-            })
+                });
+            });
         }
     }