[api-minor] Let Catalog.getAllPageDicts return an *empty* dictionary when loading the first /Page fails (issue 15590)

In order to support opening certain corrupt PDF documents, particularly hand-edited ones, this patch adds support for letting the `Catalog.getAllPageDicts` method fallback to returning an *empty* dictionary to replace (only) the first /Page of the document.
Given that the viewer cannot initialize/load without access to the first page, this will thus allow e.g. document-level scripting to run as expected. Note that by effectively replacing a corrupt or missing first /Page in this way[1], we'll now render nothing but a *blank* page for certain cases of broken/corrupt PDF documents which may look weird.

*Please note:* This functionality is controlled via the existing `stopAtErrors` option, that can be passed to `getDocument`, since it's easy to imagine use-cases where this sort of fallback behaviour isn't desirable.

---
[1] Currently we still require that a /Pages-dictionary is found though, however it *may* be possible to relax even that assumption if that becomes absolutely necessary in future corrupt documents.

src/core/catalog.js

@@ -1191,6 +1191,8 @@ class Catalog {
    * @returns {Promise<Map>}
    */
   async getAllPageDicts(recoveryMode = false) {
+    const { ignoreErrors } = this.pdfManager.evaluatorOptions;
+
     const queue = [{ currentNode: this.toplevelPagesDict, posInKids: 0 }];
     const visitedNodes = new RefSet();
 
@@ -1215,6 +1217,11 @@ class Catalog {
       if (error instanceof XRefEntryException && !recoveryMode) {
         throw error;
       }
+      if (recoveryMode && ignoreErrors && pageIndex === 0) {
+        // Ensure that the viewer will always load (fixes issue15590.pdf).
+        warn(`getAllPageDicts - Skipping invalid first page: "${error}".`);
+        error = Dict.empty;
+      }
 
       map.set(pageIndex++, [error, null]);
     }