Possible overflow in HTMLParser.c

For https://bugzilla.gnome.org/show_bug.cgi?id=720615

make sure that the encoding string passed is of reasonable size
diff --git a/HTMLparser.c b/HTMLparser.c
index 23fafb2..d329d3b 100644
--- a/HTMLparser.c
+++ b/HTMLparser.c
@@ -6288,12 +6288,16 @@
 
     /* set encoding */
     if (encoding) {
-        content = xmlMallocAtomic (xmlStrlen(content_line) + strlen(encoding) + 1);
-	if (content) {
-	    strcpy ((char *)content, (char *)content_line);
-            strcat ((char *)content, (char *)encoding);
-            htmlCheckEncoding (ctxt, content);
-	    xmlFree (content);
+        size_t l = strlen(encoding);
+
+	if (l < 1000) {
+	    content = xmlMallocAtomic (xmlStrlen(content_line) + l + 1);
+	    if (content) {
+		strcpy ((char *)content, (char *)content_line);
+		strcat ((char *)content, (char *)encoding);
+		htmlCheckEncoding (ctxt, content);
+		xmlFree (content);
+	    }
 	}
     }