pattern: Report malloc failures

Fix places where malloc failures aren't reported.

Introduce a new API function xmlPatternCompileSafe that returns a
separate error code if a memory allocation fails.

include/libxml/pattern.h

@@ -54,6 +54,12 @@ XMLPUBFUN xmlPatternPtr
 						 xmlDict *dict,
 						 int flags,
 						 const xmlChar **namespaces);
+XMLPUBFUN int
+			xmlPatternCompileSafe	(const xmlChar *pattern,
+						 xmlDict *dict,
+						 int flags,
+						 const xmlChar **namespaces,
+						 xmlPatternPtr *patternOut);
 XMLPUBFUN int
 			xmlPatternMatch		(xmlPatternPtr comp,
 						 xmlNodePtr node);