Bug#968354: xpdf crash with empty document

[Adam Sampson <ats@offog.org>]

> On Debian Bullseye this crashes xpdf with coredump:
> touch x.pdf; xpdf x.pdf

This is a Poppler bug: they've added some more sanity checks to
PDFDoc::setup, including one to catch empty files, but not all of them
set errCode correctly.

I've submitted a fix to Poppler upstream:
  https://gitlab.freedesktop.org/poppler/poppler/-/merge_requests/755

And I've added a workaround in xpopple:

--- xpdf/PDFCore.cc
+++ xpdf/PDFCore.cc
@@ -176,6 +176,13 @@ int PDFCore::loadFile2(PDFDoc *newDoc) {
   // open the PDF file
   if (!newDoc->isOk()) {
     err = newDoc->getErrorCode();
+
+    // Work around a Poppler bug: some additional checks were added to
+    // PDFDoc::setup that don't set errCode
+    if (err == errNone) {
+      err = errDamaged;
+    }
+
     delete newDoc;
     return err;
   }

Thanks very much,

-- 
Adam Sampson <ats@offog.org>                         <http://offog.org/>