Fix panic in visual line mode with folds (#10284)

Fixes: #10266



Release Notes:

- Added/Fixed/Improved ...
([#<public_issue_number_if_exists>](https://github.com/zed-industries/zed/issues/<public_issue_number_if_exists>)).

Optionally, include screenshots / media showcasing your addition that
can be included in the release notes.

**or**

- N/A

crates/vim/test_data/test_folds_panic.json

@@ -11,3 +11,13 @@
 {"Key":"d"}
 {"Key":"j"}
 {"Get":{"state":"ˇ","mode":"Normal"}}
+{"Put":{"state":"fn boop() {\n  ˇbarp()\n  bazp()\n}\n"}}
+{"Key":"shift-v"}
+{"Key":"j"}
+{"Key":"j"}
+{"Key":"z"}
+{"Key":"f"}
+{"Key":"escape"}
+{"Key":"shift-g"}
+{"Key":"shift-v"}
+{"Get":{"state":"fn boop() {\n  barp()\n  bazp()\n}\nˇ","mode":"VisualLine"}}