Don't dispatch "pagerendered"-events on the *temporary* CSS-only zooming done when drawingDelay is used (PR 15812 follow-up)

We shouldn't dispatch a "pagerendered"-event when doing *temporary* CSS-only zooming, but simply wait until the actual rendering is done.
While I don't believe that this regression has caused any actual bugs, dispatching *duplicate* events is nonetheless inconsistent and should be fixed.

web/pdf_page_view.js

@@ -616,6 +616,11 @@ class PDFPageView {
           hideTextLayer: postponeDrawing,
         });
 
+        if (postponeDrawing) {
+          // The "pagerendered"-event will be dispatched once the actual
+          // rendering is done, hence don't dispatch it here as well.
+          return;
+        }
         this.eventBus.dispatch("pagerendered", {
           source: this,
           pageNumber: this.id,