editor: Remove closed Document after updating Views

When closing a document we must wait until all views have been updated
first - either replacing their current document or closing the view -
before we remove the document from the `documents` map. The
`Editor::_refresh` helper is called by `Editor::close`. It accesses each
View's Document to sync changes and ensure that the cursor is in view.
When closing multiple Views at once, `Editor::_refresh` will attempt
to access the closing Document while refreshing a to-be-closed View.

helix-view/src/editor.rs

@@ -1816,7 +1816,6 @@ impl Editor {
         if !force && doc.is_modified() {
             return Err(CloseError::BufferModified(doc.display_name().into_owned()));
         }
-        let doc = self.documents.remove(&doc_id).unwrap();
 
         // This will also disallow any follow-up writes
         self.saves.remove(&doc_id);
@@ -1857,6 +1856,8 @@ impl Editor {
             }
         }
 
+        let doc = self.documents.remove(&doc_id).unwrap();
+
         // If the document we removed was visible in all views, we will have no more views. We don't
         // want to close the editor just for a simple buffer close, so we need to create a new view
         // containing either an existing document, or a brand new document.