Fix crash on files with forms but no AcroForm
diff --git a/poppler/Annot.cc b/poppler/Annot.cc
index e17e722..28389cc 100644
--- a/poppler/Annot.cc
+++ b/poppler/Annot.cc
@@ -1732,7 +1732,8 @@
   Object obj1;
 
   form = catalog->getForm ();
-  widget = form->findWidgetByRef (ref);
+  if (form) widget = form->findWidgetByRef (ref);
+  else widget = NULL;
 
   // check if field apperances need to be regenerated
   // Only text or choice fields needs to have appearance regenerated