[libxml2] Report error for invalid regexp quantifiers

[Nick Wellnhofer <nwellnhof src gnome org>]

commit f8329fdc234a43b858271acc75ea70881e35fcae
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Thu Jul 2 11:51:31 2020 +0200

    Report error for invalid regexp quantifiers

 xmlregexp.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/xmlregexp.c b/xmlregexp.c
index 0272dcab..687290e2 100644
--- a/xmlregexp.c
+++ b/xmlregexp.c
@@ -5268,6 +5268,9 @@ xmlFAParseQuantifier(xmlRegParserCtxtPtr ctxt) {
        cur = xmlFAParseQuantExact(ctxt);
        if (cur >= 0)
            min = cur;
+        else {
+            ERROR("Improper quantifier");
+        }
        if (CUR == ',') {
            NEXT;
            if (CUR == '}')