Clear path-based excerpt data properly (#28026)

Follow-up of https://github.com/zed-industries/zed/pull/27893

Release Notes:

- N/A

Co-authored-by: Conrad Irwin <conrad.irwin@gmail.com>

crates/multi_buffer/src/multi_buffer.rs

@@ -1719,9 +1719,7 @@ impl MultiBuffer {
                 (None, Some(_)) => {
                     let existing_id = existing_iter.next().unwrap();
                     let locator = snapshot.excerpt_locator_for_id(existing_id);
-                    let Some(existing_excerpt) = excerpts_cursor.item() else {
-                        break;
-                    };
+                    let existing_excerpt = excerpts_cursor.item().unwrap();
                     excerpts_cursor.seek_forward(&Some(locator), Bias::Left, &());
                     let existing_end = existing_excerpt
                         .range
@@ -1993,6 +1991,8 @@ impl MultiBuffer {
         self.sync(cx);
         let ids = self.excerpt_ids();
         self.buffers.borrow_mut().clear();
+        self.excerpts_by_path.clear();
+        self.paths_by_excerpt.clear();
         let mut snapshot = self.snapshot.borrow_mut();
         let start = ExcerptOffset::new(0);
         let prev_len = ExcerptOffset::new(snapshot.excerpts.summary().text.len);
@@ -2001,6 +2001,7 @@ impl MultiBuffer {
         snapshot.is_dirty = false;
         snapshot.has_deleted_file = false;
         snapshot.has_conflict = false;
+        snapshot.replaced_excerpts.clear();
 
         self.sync_diff_transforms(
             &mut snapshot,