Attach (recommended) or Link to PDF file here:

Configuration:
- Web browser and its version:
Firefox/Chrome, latest version
- Operating system and its version:
Linux,Windows,mac
- PDF.js version:
v2.12.313
- Is a browser extension:
no

Steps to reproduce the problem:
1. create a custom viewer with 
```
async function getViewer() {
const viewer = await import(/* webpackChunkName: 'pdfviewer' */ 'pdfjs-dist/web/pdf_viewer');
const eventBus = new viewer.EventBus();
return viewer.PDFSinglePageViewer({
        container,
        eventBus,
        useOnlyCssZoom: USE_ONLY_CSS_ZOOM,
        // We can enable text/annotations layers, if needed
        textLayerFactory: new viewer.DefaultTextLayerFactory(),
        annotationLayerFactory: new viewer.DefaultAnnotationLayerFactory(),
        // textLayerMode: TextLayerMode.ENABLE,
        // currently the SVG renderer is not supported
        // and it has problems with telekom documents
        // so it will be disabled until it is feature complete
        // renderer: 'svg'
    });
}
```
2. console prints an error:
```
Unable to get page for page view TypeError: this.linkService._cachedPageNumber is not a function
    ensurePdfPageLoaded_fn base_viewer.js:1502
```
    
Looks like the problem is `IPDFLinkService` which is actually using the default one `this.linkService = options.linkService || new SimpleLinkService();` which does not have this function. of course we can use `PDFLinkService` which will probably work.

pagesCount > PagesCountLimit.FORCE_LAZY_PAGE_INIT
          ) {
            
            this._pagesCapability.resolve();
            return;
          }
          let getPagesLeft = pagesCount - 1; 
          if (getPagesLeft <= 0) {
            this._pagesCapability.resolve();
            return;
          }
          for (let pageNum = 2; pageNum <= pagesCount; ++pageNum) {
            const promise = pdfDocument.getPage(pageNum).then(
              pdfPage => {
                const pageView = this._pages[pageNum - 1];
                if (!pageView.pdfPage) {
                  pageView.setPdfPage(pdfPage);
                }
                this.linkService.cachePageRef(pageNum, pdfPage.ref);
                if (--getPagesLeft === 0) {
                  this._pagesCapability.resolve();
                }
              },
              reason => {
                console.error(
                  `Unable to get page ${pageNum} to initialize viewer`,
                  reason
                );
                if (--getPagesLeft === 0) {
                  this._pagesCapability.resolve();