Initialize outputFormats to the empty list

outputFormats is derived from sequencing language adaptation, but
starts out as undefined. This commit protects any code that assumes
it's always a list.

src/components/sequencing/SequenceEditor.svelte

@@ -100,7 +100,7 @@
   let editorSequenceDiv: HTMLDivElement;
   let editorSequenceView: EditorView;
   let menu: Menu;
-  let outputFormats: IOutputFormat[];
+  let outputFormats: IOutputFormat[] = [];
   let selectedNode: SyntaxNode | null;
   let currentTree: Tree;
   let commandInfoMapper: CommandInfoMapper = new SeqNCommandInfoMapper();