Fix a hang issue due to inconsistent page number in the test file

Pdfium reads the page number from the field of '/Count' but it can't
load the number assigned by this field due to the damaged data. Add a
check to ensure that the required page should be one of loaded pages.

BUG=406090
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/477873003

core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp

diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
index e0fd3bf..ce397d2 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
@@ -3989,7 +3989,7 @@
 FX_BOOL CPDF_DataAvail::CheckPageNode(CPDF_PageNode &pageNodes, FX_INT32 iPage, FX_INT32 &iCount, IFX_DownloadHints* pHints)
 {
     FX_INT32 iSize = pageNodes.m_childNode.GetSize();
-    if (!iSize) {
+    if (iSize <= 0 || iPage >= iSize) {
         m_docStatus = PDF_DATAAVAIL_ERROR;
         return FALSE;
     }

samples/pdfium_test.cc

diff --git a/samples/pdfium_test.cc b/samples/pdfium_test.cc
index 72c8c5d..7436e9d 100644
--- a/samples/pdfium_test.cc
+++ b/samples/pdfium_test.cc
@@ -304,8 +304,14 @@
   FORM_DoDocumentJSAction(form);
   FORM_DoDocumentOpenAction(form);
 
+  size_t rendered_pages = 0;
+  size_t bad_pages = 0;
   for (int i = 0; i < page_count; ++i) {
     FPDF_PAGE page = FPDF_LoadPage(doc, i);
+    if (!page) {
+        bad_pages ++;
+        continue;
+    }
     FPDF_TEXTPAGE text_page = FPDFText_LoadPage(page);
     FORM_OnAfterLoadPage(page, form);
     FORM_DoPageAAction(page, form, FPDFPAGE_AACTION_OPEN);
@@ -316,6 +322,8 @@
     FPDFBitmap_FillRect(bitmap, 0, 0, width, height, 0xFFFFFFFF);
 
     FPDF_RenderPageBitmap(bitmap, page, 0, 0, width, height, 0, 0);
+    rendered_pages ++;
+
     FPDF_FFLDraw(form, bitmap, page, 0, 0, width, height, 0, 0);
     int stride = FPDFBitmap_GetStride(bitmap);
     const char* buffer =
@@ -351,7 +359,8 @@
   FPDF_CloseDocument(doc);
   FPDFAvail_Destroy(pdf_avail);
 
-  printf("Loaded, parsed and rendered %d pages.\n", page_count);
+  printf("Loaded, parsed and rendered %d pages.\n", rendered_pages);
+  printf("Skipped %d bad pages.\n", bad_pages);
 }
 
 int main(int argc, const char* argv[]) {