fix(scrolling): virtual scroll viewport returning range larger than data when switching to smaller set

Fixes the `VirtualScrollViewport.getRenderedRange` returning a range that is larger than the data when we switch to a smaller set. I decided to do this in the viewport, rather than the strategy so we don't have to repeat the same logic in each of the strategies.

Fixes #19029.

Author: crisbeto

src/cdk/scrolling/virtual-scroll-viewport.spec.ts

@@ -100,6 +100,22 @@ describe('CdkVirtualScrollViewport', () => {
           .toEqual({start: 0, end: 4}, 'should render the first 4 50px items to fill 200px space');
     }));
 
+    it('should contract the rendered range when changing to less data', fakeAsync(() => {
+      finishInit(fixture);
+
+      expect(viewport.getRenderedRange()).toEqual({start: 0, end: 4});
+
+      fixture.componentInstance.items = [0, 1];
+      fixture.detectChanges();
+
+      expect(viewport.getRenderedRange()).toEqual({start: 0, end: 2});
+
+      fixture.componentInstance.items = [];
+      fixture.detectChanges();
+
+      expect(viewport.getRenderedRange()).toEqual({start: 0, end: 0});
+    }));
+
     it('should get the rendered content offset', fakeAsync(() => {
       finishInit(fixture);
       triggerScroll(viewport, testComponent.itemSize + 5);

src/cdk/scrolling/virtual-scroll-viewport.ts

@@ -277,6 +277,9 @@ export class CdkVirtualScrollViewport extends CdkScrollable implements OnInit, O
 
   /** Sets the currently rendered range of indices. */
   setRenderedRange(range: ListRange) {
+    // The range should never be greater than the data.
+    range.end = Math.min(range.end, this.getDataLength());
+
     if (!rangesEqual(this._renderedRange, range)) {
       this._renderedRangeSubject.next(this._renderedRange = range);
       this._markChangeDetectionNeeded(() => this._scrollStrategy.onContentRendered());