Attached fuzzed PDF from Sauli Pahlman crashes poppler at or around DCTStream::reset.  The reason for the crash is that the file contains a truncated JPEG image which does not contain full image header.  jpeg_read_header() called from DCTStream::reset returns JPEG_SUSPENDED and some of the cinfo struct members are not properly set, causing a NULL pointer dereference crash on this specific file.

This change avoids the crash on this file:

index 78cd59d..e96ec5a 100644
--- a/poppler/DCTStream.cc
+++ b/poppler/DCTStream.cc
@@ -141,8 +141,7 @@ void DCTStream::reset() {
     }
   }
 
-  if (!setjmp(err.setjmp_buffer)) {
-    jpeg_read_header(&cinfo, TRUE);
+  if (!setjmp(err.setjmp_buffer) && jpeg_read_header(&cinfo, TRUE) != JPEG_SUSPENDED) {
 
     // figure out color transform
     if (colorXform == -1 && !cinfo.saw_Adobe_marker) {