preserve previous options

docs/app/js/sanddance-app.js

@@ -151179,7 +151179,7 @@ class Explorer extends React.Component {
   }
 
   updateViewerOptions(viewerOptions) {
-    this.viewerOptions = Object.assign({}, viewerOptions, {
+    this.viewerOptions = Object.assign({}, this.viewerOptions, viewerOptions, {
       onColorContextChange: () => this.manageColorToolbar(),
       onDataFilter: (dataFilter, filteredData) => {
         const selectedItemIndex = Object.assign({}, this.state.selectedItemIndex);

packages/sanddance-explorer/src/explorer.tsx

@@ -143,6 +143,7 @@ export class Explorer extends React.Component<Props, State> {
 
   public updateViewerOptions(viewerOptions: Partial<SandDance.types.ViewerOptions>) {
     this.viewerOptions = {
+      ...this.viewerOptions,
       ...viewerOptions,
       onColorContextChange: () => this.manageColorToolbar(),
       onDataFilter: (dataFilter, filteredData) => {