git_graph: Fix empty search case (#52845)

This fixes a bug where search would match all commits if there was an empty query instead of setting the query to None

Self-Review Checklist:

- [ ] I've reviewed my own diff for quality, security, and reliability
- [ ] Unsafe blocks (if any) have justifying comments
- [ ] The content is consistent with the [UI/UX
checklist](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
- [ ] Tests cover the new/changed behavior
- [ ] Performance impact has been considered and is acceptable

Closes #ISSUE

Release Notes:

- N/A or Added/Fixed/Improved ...

---------

Co-authored-by: Remco Smits <djsmits12@gmail.com>

crates/git_graph/src/git_graph.rs

@@ -1324,6 +1324,12 @@ impl GitGraph {
             editor.set_text_style_refinement(Default::default());
         });
 
+        if query.as_str().is_empty() {
+            self.search_state.state = QueryState::Empty;
+            cx.notify();
+            return;
+        }
+
         let (request_tx, request_rx) = smol::channel::unbounded::<Oid>();
 
         repo.update(cx, |repo, cx| {