Ensure that attempting to print with disableAutoFetch set will fail…

… gracefully (issue 11339)

This patch simply restores the behaviour that existed prior to PR 7697, since I cannot imagine that that was changed other than by pure accident.
As mentioned by a comment in `BaseViewer.setDocument`: "Printing is semi-broken with auto fetch disabled.", and note that since triggering of printing is a *synchronous* operation there's no generally easy way load the missing data.

web/base_viewer.js

@@ -181,7 +181,14 @@ class BaseViewer {
    * @type {boolean} - True if all {PDFPageView} objects are initialized.
    */
   get pageViewsReady() {
-    return this._pageViewsReady;
+    if (!this._pageViewsReady) {
+      return false;
+    }
+    // Prevent printing errors when 'disableAutoFetch' is set, by ensuring
+    // that *all* pages have in fact been completely loaded.
+    return this._pages.every(function(pageView) {
+      return !!(pageView && pageView.pdfPage);
+    });
   }
 
   /**