Some warning fixes.
Fixed this error:
Debug info: Argument 1 passed to booking_generate_email_params() must be an instance of stdClass, null given, called in [dirroot]/mod/booking/lib.php on line 1625 and defined
Error code: codingerror
Stack trace:
line 393 of /lib/setuplib.php: coding_exception thrown
line 1719 of /mod/booking/lib.php: call to default_error_handler()
line 1625 of /mod/booking/lib.php: call to booking_generate_email_params()
line 291 of /mod/booking/locallib.php: call to booking_send_confirm_message()
line 92 of /mod/booking/subscribeusers.php: call to booking_option->user_submit_response()