Fix assertion triggered when mediaserver dies at roughly the same

    OMXNodeInstance *instance = findInstance(node);

    ssize_t index = mLiveNodes.indexOfKey(instance->observer()->asBinder());

    CHECK(index >= 0);

    if (index < 0) {

        // This could conceivably happen if the observer dies at roughly the

        // same time that a client attempts to free the node explicitly.

        return OK;

    }

    mLiveNodes.removeItemsAt(index);

    instance->observer()->asBinder()->unlinkToDeath(this);