Fix: validateDTD compile fails if when libxml2 not installed

Author: martinhsv

CHANGES

@@ -1,6 +1,8 @@
 v3.x.y - YYYY-MMM-DD (to be released)
 -------------------------------------
 
+  - Fix: validateDTD compile fails if when libxml2 not installed
+    [Issue #3014 - @zangobot, @martinhsv]
   - Fix memory leak of validateDTD's dtd object
     [Issue #3008 - @martinhsv, @zimmerle]
   - Fix memory leaks in ValidateSchema

src/operators/validate_dtd.h

@@ -33,23 +33,23 @@
 namespace modsecurity {
 namespace operators {
 
+#ifdef WITH_LIBXML2
 class XmlDtdPtrManager {
  public:
     /** @ingroup ModSecurity_Operator */
     explicit XmlDtdPtrManager(xmlDtdPtr dtd)
         : m_dtd(dtd) { }
     ~XmlDtdPtrManager() {
-#ifdef WITH_LIBXML2
         if (m_dtd != NULL) {
             xmlFreeDtd(m_dtd);
             m_dtd = NULL;
         }
-#endif
     }
     xmlDtdPtr get() const {return m_dtd;}
  private:
     xmlDtdPtr m_dtd; // The resource being managed
 };
+#endif
 
 class ValidateDTD : public Operator {
  public: