Make trackUploadDesign more robust

Fall back to empty array for designs
in response.

app/assets/javascripts/design_management/pages/index.vue

@@ -204,7 +204,7 @@ export default {
       this.trackUploadDesign(res);
     },
     trackUploadDesign(res) {
-      res.data.designManagementUpload.designs.forEach(design => {
+      (res?.data?.designManagementUpload?.designs || []).forEach(design => {
         if (design.event === 'CREATION') {
           trackDesignCreate();
         } else if (design.event === 'MODIFICATION') {

spec/frontend/design_management/pages/index_spec.js

@@ -374,7 +374,7 @@ describe('Design management index page', () => {
       createComponent({ stubs: { GlEmptyState } });
       wrapper.setData({ filesToBeSaved: [{ name: 'test' }] });
 
-      wrapper.vm.onUploadDesignDone();
+      wrapper.vm.onUploadDesignDone(designUploadMutationCreatedResponse);
       return wrapper.vm.$nextTick().then(() => {
         expect(wrapper.vm.filesToBeSaved).toEqual([]);
         expect(wrapper.vm.isSaving).toBeFalsy();