Fix CVE-2021-3500: Stack-Based Buffer Overflow
https://bugzilla.redhat.com/show_bug.cgi?id=1943411

Index: libdjvu/DjVuPort.h
--- libdjvu/DjVuPort.h.orig
+++ libdjvu/DjVuPort.h
@@ -484,6 +484,7 @@ class DJVUAPI DjVuPortcaster (private)
                        const DjVuPort *dst, int distance);
    void compute_closure(const DjVuPort *src, GPList<DjVuPort> &list,
                         bool sorted=false);
+   GUTF8String opening_id;
 };
 
 
