Don't check qobject_type() before qobject_to_qdict()

qobject_to_qdict(obj) returns NULL when obj isn't a QDict.  Check
that instead of qobject_type(obj) == QTYPE_QDICT.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <1487363905-9480-8-git-send-email-armbru@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
diff --git a/block.c b/block.c
index 743c349..3c36af5 100644
--- a/block.c
+++ b/block.c
@@ -1169,13 +1169,13 @@
         return NULL;
     }
 
-    if (qobject_type(options_obj) != QTYPE_QDICT) {
+    options = qobject_to_qdict(options_obj);
+    if (!options) {
         qobject_decref(options_obj);
         error_setg(errp, "Invalid JSON object given");
         return NULL;
     }
 
-    options = qobject_to_qdict(options_obj);
     qdict_flatten(options);
 
     return options;