Avoid panic from assuming a vim operator exists on the operator stack (#2773)

Fixes
https://linear.app/zed-industries/issue/Z-338/operator-popped-when-no-operator-was-on-the-stack-this-likely-means

Release Notes:
- Fixed a panic that could occur when invoking a Vim object without an
operator.
e002d9efb0Julia committed on 7/21/2023, 6:47:38 PM· committed by GitHubparents56c657f243a1a8
1 file changedLine totals unavailable