Fix "Show toolbar" bug

During the migration to NNBD a bug occurred that prevents the toolbar from
being displayed. The code changes revert to the original code without bug.

lib/widgets/raw_editor.dart

@@ -1094,7 +1094,6 @@ class RawEditorState extends EditorState
 
   @override
   bool showToolbar() {
-    if (_selectionOverlay == null || _selectionOverlay!.toolbar != null) {
     // Web is using native dom elements to enable clipboard functionality of the
     // toolbar: copy, paste, select, cut. It might also provide additional
     // functionality depending on the browser (such as translate). Due to this
@@ -1102,7 +1101,6 @@ class RawEditorState extends EditorState
     if (kIsWeb) {
       return false;
     }
-
     if (_selectionOverlay == null || _selectionOverlay!.toolbar != null) {
       return false;
     }
@@ -1110,8 +1108,6 @@ class RawEditorState extends EditorState
     _selectionOverlay!.showToolbar();
     return true;
   }
-    return true;
-  }
 
   @override
   bool get wantKeepAlive => widget.focusNode.hasFocus;