Fix security issue CVE-2016-10040

[taken from RedHat Qt3 patches]

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>
(cherry picked from commit 54809cd81b)

src/xml/qxml.h

@@ -311,7 +311,7 @@ private:
     // for the DTD currently being parsed.
     static const uint dtdRecursionLimit = 2U;
     // The maximum amount of characters an entity value may contain, after expansion.
-    static const uint entityCharacterLimit = 65536U;
+    static const uint entityCharacterLimit = 4096U;
 
     const QString &string();
     void stringClear();