Fix weird streaming RelaxNG errors

For https://bugzilla.gnome.org/show_bug.cgi?id=512454
The bug was to use compiled determinitic automata when
the content model was found to be non-deterministic, leading
to random parsing errors.
diff --git a/relaxng.c b/relaxng.c
index f575287..18f6a0b 100644
--- a/relaxng.c
+++ b/relaxng.c
@@ -3059,8 +3059,8 @@
                     list = list->next;
                 }
                 xmlAutomataSetFinalState(ctxt->am, ctxt->state);
-                def->contModel = xmlAutomataCompile(ctxt->am);
-                xmlRegexpIsDeterminist(def->contModel);
+                if (xmlAutomataIsDeterminist(ctxt->am))
+                    def->contModel = xmlAutomataCompile(ctxt->am);
 
                 xmlFreeAutomata(ctxt->am);
                 ctxt->state = oldstate;