Fix protect bug

Author: jeroen

src/xml2_utils.h

@@ -14,11 +14,12 @@ enum NodeType {
 
 
 inline int inherits3(SEXP x, const char *name) {
-  SEXP expr = PROTECT(Rf_lang3(Rf_install("inherits"), x, Rf_mkString(name)));
+  SEXP arg = PROTECT(Rf_mkString(name));
+  SEXP expr = PROTECT(Rf_lang3(Rf_install("inherits"), x, arg));
   SEXP result = PROTECT(Rf_eval(expr, R_GlobalEnv));
 
   int out = LOGICAL(result)[0];
-  UNPROTECT(2);
+  UNPROTECT(3);
   return out;
 }