Fix: unsafe operation while getting overlayEntry in text_selection (#2117)

* Fix: unsafe operation while getting a overlay entry in text selection

* Chore: dart format

---------

Co-authored-by: CatHood0 <santiagowmar@gmail.com>

lib/src/editor/widgets/text/text_selection.dart

@@ -433,7 +433,7 @@ class EditorTextSelectionOverlay {
       context: context,
       below: magnifierConfiguration.shouldDisplayHandlesInMagnifier
           ? null
-          : _handles![0],
+          : _handles?.elementAtOrNull(0),
       builder: (_) => builtMagnifier,
     );
   }