registry: Restore default libxml2 error handler after parsing

Leaving the custom error handler could have resulted in a crash after
the context has been freed.

Closes: #529

Author: sbstnk

src/registry.c

@@ -1264,6 +1264,7 @@ parse(struct rxkb_context *ctx, const char *path,
     success = true;
 error:
     xmlFreeDoc(doc);
+    xmlSetGenericErrorFunc(NULL, NULL);
 
     return success;
 }