Fix crash with unexpected DTD nodes in XSLT.

third_party/libxslt/libxslt/xsltutils.h

 /*
  * Summary: set of utilities for the XSLT engine
  * Description: interfaces for the utilities module of the XSLT engine.
  *              things like message handling, profiling, and other
  *              generally useful routines.
  *
  * Copy: See Copyright for the status of this software.
  *
  * Author: Daniel Veillard
  */
@@ skipping 34 matching lines @@
     xsltGenericError(xsltGenericErrorContext,                           \
             "Internal error at %s:%d\n",                                \
             __FILE__, __LINE__);
 
 /**
  * IS_XSLT_ELEM:
  *
  * Checks that the element pertains to XSLT namespace.
  */
 #define IS_XSLT_ELEM(n)                                                 \
-    (((n) != NULL) && ((n)->ns != NULL) &&                              \
-     (xmlStrEqual((n)->ns->href, XSLT_NAMESPACE)))
+    (((n) != NULL) && ((n)->type == XML_ELEMENT_NODE) &&                \
+     ((n)->ns != NULL) && (xmlStrEqual((n)->ns->href, XSLT_NAMESPACE)))
 
 /**
  * IS_XSLT_NAME:
  *
  * Checks the value of an element in XSLT namespace.
  */
 #define IS_XSLT_NAME(n, val)                                            \
     (xmlStrEqual((n)->name, (const xmlChar *) (val)))
 
 /**
@@ skipping 233 matching lines @@
 XSLTPUBFUN void XSLTCALL                
                 xslDropCall                     (void);
 
 #ifdef __cplusplus
 }
 #endif
 
 #endif /* __XML_XSLTUTILS_H__ */