Show '-' if there is no reserving user ID for a booking

Author: mlt47

src/app/components/elements/panels/ManageExistingBookings.tsx

@@ -159,7 +159,7 @@ export const ManageExistingBookings = ({user, eventBookingId}: {user: LoggedInUs
                                     <td className="align-middle"><DateString>{booking.bookingDate}</DateString></td>
                                     <td className="align-middle"><DateString>{booking.updated}</DateString></td>
                                     {SITE_SUBJECT == SITE.CS && <td className="align-middle">{booking.userBooked && booking.userBooked.examBoard}</td>}
-                                    <td className="align-middle text-center">{booking.reservedById}</td>
+                                    <td className="align-middle text-center">{booking.reservedById || "-"}</td>
                                     <td className="align-middle">{booking.additionalInformation && booking.additionalInformation.experienceLevel}</td>
                                     <td className="align-middle">{booking.additionalInformation && booking.additionalInformation.accessibilityRequirements}</td>
                                     <td className="align-middle">{booking.additionalInformation && booking.additionalInformation.medicalRequirements}</td>