refactor(ui/explorer/close_documents): concise code

Resolve https://github.com/helix-editor/helix/pull/5768#discussion_r1133065427

helix-term/src/ui/explorer.rs

@@ -755,11 +755,7 @@ fn close_documents(current_item_path: PathBuf, cx: &mut Context) -> Result<()> {
         .documents
         .iter()
         .filter_map(|(id, doc)| {
-            if doc
+            if doc.path()?.starts_with(&current_item_path) {
-                .path()
-                .map(|p| p.starts_with(&current_item_path))
-                .unwrap_or(false)
-            {
                 Some(*id)
             } else {
                 None