Update getWindowConfig to handle missing windows

__tests__/src/selectors/windows.test.js

@@ -24,6 +24,18 @@ describe('getWindowConfig', () => {
 
     expect(getWindowConfig(state, { windowId: 'a' })).toEqual({ a: '1', b: '3', c: '4' });
   });
+  it('gracefully handles missing windows', () => {
+    const state = {
+      config: {
+        window: { a: '1', b: '2' },
+      },
+      windows: {
+        a: {},
+      },
+    };
+
+    expect(getWindowConfig(state, { windowId: 'c' })).toEqual({ a: '1', b: '2' });
+  });
 });
 
 describe('getMaximizedWindowsIds', () => {

src/state/selectors/windows.js

@@ -10,7 +10,7 @@ import { getSequenceViewingHint, getSequenceBehaviors } from './sequences';
 /** */
 export const getWindowConfig = createSelector(
   [getConfig, getWindow],
-  ({ window: defaultConfig }, windowConfig) => ({ ...defaultConfig, ...windowConfig }),
+  ({ window: defaultConfig }, windowConfig = {}) => ({ ...defaultConfig, ...windowConfig }),
 );
 
 /**