Fixes a panic at `Editor::text_layout_details` when called against an
editor whose element has never been laid out (i.e., `set_style` has
never been called, so the cached `style` is still `None`).

We've seen this crash once through a helix motion. The exact production
sequence isn't clear — for the editor to receive a vim action without
ever having been drawn, the active item would have to have changed
inside the same update tick that ends with the deferred `search_submit`,
which is narrow but not impossible (since it's dispatched by the
workspace, not the editor).

Release Notes:

- Fixed a rare panic when invoking helix motions on an editor that had
not yet been laid out.