[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]);
     }

test/unit/api_spec.js

@@ -602,27 +602,42 @@ describe("api", function () {
       const loadingTask2 = getDocument(
         buildGetDocumentParams("poppler-85140-0.pdf")
       );
+      const loadingTask3 = getDocument(
+        buildGetDocumentParams("poppler-85140-0.pdf", { stopAtErrors: true })
+      );
 
       expect(loadingTask1 instanceof PDFDocumentLoadingTask).toEqual(true);
       expect(loadingTask2 instanceof PDFDocumentLoadingTask).toEqual(true);
+      expect(loadingTask3 instanceof PDFDocumentLoadingTask).toEqual(true);
 
       const pdfDocument1 = await loadingTask1.promise;
       const pdfDocument2 = await loadingTask2.promise;
+      const pdfDocument3 = await loadingTask3.promise;
 
       expect(pdfDocument1.numPages).toEqual(1);
       expect(pdfDocument2.numPages).toEqual(1);
+      expect(pdfDocument3.numPages).toEqual(1);
 
-      const page = await pdfDocument1.getPage(1);
-      expect(page instanceof PDFPageProxy).toEqual(true);
+      const pageA = await pdfDocument1.getPage(1);
+      expect(pageA instanceof PDFPageProxy).toEqual(true);
 
-      const opList = await page.getOperatorList();
-      expect(opList.fnArray.length).toBeGreaterThan(5);
-      expect(opList.argsArray.length).toBeGreaterThan(5);
-      expect(opList.lastChunk).toEqual(true);
-      expect(opList.separateAnnots).toEqual(null);
+      const opListA = await pageA.getOperatorList();
+      expect(opListA.fnArray.length).toBeGreaterThan(5);
+      expect(opListA.argsArray.length).toBeGreaterThan(5);
+      expect(opListA.lastChunk).toEqual(true);
+      expect(opListA.separateAnnots).toEqual(null);
+
+      const pageB = await pdfDocument2.getPage(1);
+      expect(pageB instanceof PDFPageProxy).toEqual(true);
+
+      const opListB = await pageB.getOperatorList();
+      expect(opListB.fnArray.length).toBe(0);
+      expect(opListB.argsArray.length).toBe(0);
+      expect(opListB.lastChunk).toEqual(true);
+      expect(opListB.separateAnnots).toEqual(null);
 
       try {
-        await pdfDocument2.getPage(1);
+        await pdfDocument3.getPage(1);
 
         // Shouldn't get here.
         expect(false).toEqual(true);
@@ -631,7 +646,11 @@ describe("api", function () {
         expect(reason.message).toEqual("Bad (uncompressed) XRef entry: 3R");
       }
 
-      await Promise.all([loadingTask1.destroy(), loadingTask2.destroy()]);
+      await Promise.all([
+        loadingTask1.destroy(),
+        loadingTask2.destroy(),
+        loadingTask3.destroy(),
+      ]);
     });
 
     it("creates pdf doc from PDF files, with circular references", async function () {
@@ -751,17 +770,8 @@ describe("api", function () {
         OpenAction: ["func=function(){app.alert(1)};func();"],
       });
 
-      try {
-        await pdfDocument.getPage(1);
-
-        // Shouldn't get here.
-        expect(false).toEqual(true);
-      } catch (reason) {
-        expect(reason instanceof UnknownErrorException).toEqual(true);
-        expect(reason.message).toEqual(
-          "Page dictionary kids object is not an array."
-        );
-      }
+      const page = await pdfDocument.getPage(1);
+      expect(page instanceof PDFPageProxy).toEqual(true);
 
       await loadingTask.destroy();
     });