qapi: Make QObject input visitor set *list reliably

qobject_input_start_struct() sets *list, except when it fails because
qobject_input_get_object() fails, i.e. the input object doesn't exist.

All the other input visitor start_struct(), start_list(),
start_alternate() always set *obj / *list.

Change qobject_input_start_struct() to match.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Message-Id: <1488544368-30622-14-git-send-email-armbru@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>

qapi/qobject-input-visitor.c

@@ -196,25 +196,21 @@ static void qobject_input_start_list(Visitor *v, const char *name,
     QObject *qobj = qobject_input_get_object(qiv, name, true, errp);
     const QListEntry *entry;
 
+    if (list) {
+        *list = NULL;
+    }
     if (!qobj) {
         return;
     }
     if (qobject_type(qobj) != QTYPE_QLIST) {
-        if (list) {
-            *list = NULL;
-        }
         error_setg(errp, QERR_INVALID_PARAMETER_TYPE, name ? name : "null",
                    "list");
         return;
     }
 
     entry = qobject_input_push(qiv, qobj, list);
-    if (list) {
-        if (entry) {
-            *list = g_malloc0(size);
-        } else {
-            *list = NULL;
-        }
+    if (entry && list) {
+        *list = g_malloc0(size);
     }
 }