bp_messages_enforce_current_user( array|string $args = array() )

function bp_messages_enforce_current_user( $args = array() ) {

	// Non-community moderators can only ever see their own messages.
	if ( is_user_logged_in() && ! bp_current_user_can( 'bp_moderate' ) ) {
		$_user_id = (int) bp_loggedin_user_id();
		if ( $_user_id !== (int) $args['user_id'] ) {
			$args['user_id'] = $_user_id;
		}
	}

	// Return possibly modified $args array.
	return $args;
}