fix schema validation in combination with xsi:nil

Based on Thomas Gamper <icicle@cg.tuwien.ac.at> findings and
initial patch

There is no point doing a regexp validation of further
content if there actually is no further content because the
element is nilled.

xmlschemas.c

@@ -26063,6 +26063,20 @@ xmlSchemaValidatorPopElem(xmlSchemaValidCtxtPtr vctxt)
 		    "AUTOMATON create on '%s'\n", inode->localName);
 #endif
 	    }
+
+	    /*
+	     * Do not check further content if the node has been nilled
+	     */
+	    if (INODE_NILLED(inode)) {
+		ret = 0;
+#ifdef DEBUG_AUTOMATA
+		xmlGenericError(xmlGenericErrorContext,
+		    "AUTOMATON succeeded on nilled '%s'\n",
+		    inode->localName);
+#endif
+                goto skip_nilled;
+	    }
+
 	    /*
 	    * Get hold of the still expected content, since a further
 	    * call to xmlRegExecPushString() will loose this information.
@@ -26100,6 +26114,9 @@ xmlSchemaValidatorPopElem(xmlSchemaValidCtxtPtr vctxt)
 
 	}
     }
+
+skip_nilled:
+
     if (inode->typeDef->contentType == XML_SCHEMA_CONTENT_ELEMENTS)
 	goto end_elem;