Fix crash in PDF accessibility when PDF engine reports -1 as char count.

pdf/out_of_process_instance.cc

Index: pdf/out_of_process_instance.cc
diff --git a/pdf/out_of_process_instance.cc b/pdf/out_of_process_instance.cc
index bc0fb5b6c283d21ab47a559271489820a5a8cf46..5d90b39620b55a0d1834550f98e12d208eb1f3b6 100644
--- a/pdf/out_of_process_instance.cc
+++ b/pdf/out_of_process_instance.cc
@@ -747,6 +747,12 @@ void OutOfProcessInstance::SendNextAccessibilityPage(int32_t page_index) {
     return;
 
   int char_count = engine_->GetCharCount(page_index);
+
+  // Treat a char count of -1 (error) as 0 (an empty page), since
+  // other pages might have valid content.
+  if (char_count < 0)
+    char_count = 0;
+
   PP_PrivateAccessibilityPageInfo page_info;
   page_info.page_index = page_index;
   page_info.bounds = engine_->GetPageBoundsRect(page_index);