Guard against empty canvas groupings. Related to #3543 (#3545)

Author: cbeer

__tests__/src/components/ThumbnailNavigation.test.js

@@ -100,6 +100,12 @@ describe('ThumbnailNavigation', () => {
       expect(wrapper.instance().areaHeight()).toEqual(150);
       expect(rightWrapper.instance().areaHeight(99)).toEqual(99);
     });
+    describe('without any canvases', () => {
+      it('returns the default for the calculated size', () => {
+        wrapper = createWrapper({ canvasGroupings: new CanvasGroupings([]).groupings() });
+        expect(wrapper.instance().calculateScaledSize(0)).toEqual(108);
+      });
+    });
   });
   describe('keyboard navigation', () => {
     const setNextCanvas = jest.fn();

src/components/ThumbnailNavigation.js

@@ -69,7 +69,9 @@ export class ThumbnailNavigation extends Component {
    */
   calculateScaledSize(index) {
     const { thumbnailNavigation, canvasGroupings, position } = this.props;
-    const canvases = canvasGroupings[index] || [];
+    const canvases = canvasGroupings[index];
+    if (!canvases) return thumbnailNavigation.width + this.spacing;
+
     const world = new CanvasWorld(canvases);
     const bounds = world.worldBounds();
     switch (position) {

src/lib/CanvasWorld.js

@@ -203,8 +203,8 @@ export default class CanvasWorld {
    * lined up horizontally starting from left to right.
    */
   worldBounds() {
-    const worldWidth = Math.max(...this.canvasDimensions.map(c => c.x + c.width));
-    const worldHeight = Math.max(...this.canvasDimensions.map(c => c.y + c.height));
+    const worldWidth = Math.max(0, ...this.canvasDimensions.map(c => c.x + c.width));
+    const worldHeight = Math.max(0, ...this.canvasDimensions.map(c => c.y + c.height));
 
     return [
       0,