qom: Make "object" QemuOptsList optional

This code is going away anyway, but for a few more commits, we'll be in
a state where some binaries still use QemuOpts and others don't. If the
"object" QemuOptsList doesn't even exist, we don't have to remove (or
fail to remove, and therefore abort) a user creatable object from it.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

qom/object_interfaces.c

@@ -299,6 +299,7 @@ void user_creatable_print_help_from_qdict(QDict *args)
 
 bool user_creatable_del(const char *id, Error **errp)
 {
+    QemuOptsList *opts_list;
     Object *container;
     Object *obj;
 
@@ -318,8 +319,10 @@ bool user_creatable_del(const char *id, Error **errp)
      * if object was defined on the command-line, remove its corresponding
      * option group entry
      */
-    qemu_opts_del(qemu_opts_find(qemu_find_opts_err("object", &error_abort),
-                                 id));
+    opts_list = qemu_find_opts_err("object", NULL);
+    if (opts_list) {
+        qemu_opts_del(qemu_opts_find(opts_list, id));
+    }
 
     object_unparent(obj);
     return true;