`/new` with invalid `references` value causes unexpected error

[eartharoid]

because this line doesn't check if the referenced ticket exists

bot/src/lib/tickets/manager.js

Line 635 in 22e26e1

if (referencesTicketId) data.referencesTicket = { connect: { id: referencesTicketId } };

which happens earlier but is out of scope

bot/src/lib/tickets/manager.js

Lines 589 to 590 in 22e26e1

	const ticket = await this.client.prisma.ticket.findUnique({ where: { id: referencesTicketId } });
	if (ticket) {