Prepend username on any files uploaded with WP Job Manager

functions.php

<?php

add_filter( 'job_manager_upload_file_pre_upload', 'smyles_add_user_login_to_file_uploads' );

function smyles_add_user_login_to_file_uploads( $file ) {

	$user = wp_get_current_user();
	if ( $user && $user->ID > 0 ) {
		$file['name'] = sanitize_file_name( $user->user_login ) . '_' . $file['name'];
	}

	return $file;
}