Fix for canvases with no annotations

When using the Search feature, switching to a canvas without a search
hit (i.e. no annotations targeting it), Mirador would run into a
`TypeError` in the `setCurrentAnnotationsOnCurrentCanvas` saga.
The underlying cause was that the code would try to select the first
annotation for the current canvas, if the currently selected annotation
was not targeting it. This, of course, failed when there were no
annotations targeting the current canvas.

This commit fixes it by adding a check for the presence of annotations
for the current canvas before dispatching the `selectAnnotation`
action.

__tests__/src/sagas/windows.test.js

@@ -221,6 +221,28 @@ describe('window-level sagas', () => {
         .then(({ allEffects }) => allEffects.length === 0);
     });
 
+    it('does nothing when there are no annotations targeting the current canvas', () => {
+      const action = {
+        type: ActionTypes.SET_CANVAS,
+        visibleCanvases: ['a', 'b'],
+        windowId: 'abc123',
+      };
+
+      return expectSaga(setCurrentAnnotationsOnCurrentCanvas, action)
+        .provide([
+          [select(getSearchForWindow,
+            { windowId: 'abc123' }), { cwid: { } }],
+          [select(getAnnotationsBySearch, { canvasIds: ['a', 'b'], companionWindowIds: ['cwid'], windowId: 'abc123' }),
+            { }],
+        ])
+        .run()
+        // Assert that nothing did happen, see https://github.com/jfairbank/redux-saga-test-plan/issues/137
+        .then(({ effects }) => {
+          expect(effects.select.length).toEqual(2);
+          expect(effects.put).toBeUndefined();
+        });
+    });
+
     it('selects content search annotations for the current searches', () => {
       const action = {
         type: ActionTypes.SET_CANVAS,

src/state/sagas/windows.js

@@ -129,9 +129,11 @@ export function* setCurrentAnnotationsOnCurrentCanvas({
         )))),
   );
 
+  if (Object.values(annotationBySearch).length > 0) {
     // if the currently selected annotation isn't on this canvas, do a thing.
     yield put(selectAnnotation(windowId, Object.values(annotationBySearch)[0][0]));
   }
+}
 
 /** @private */
 export function* panToFocusedWindow({ pan, windowId }) {