LOWELL — Someday, Jim Tessier and Lah Chomthakham may joke about how some of their careful wedding plans went sideways, but right now, they’re not laughing. The couple, who is getting married on Oct. 7 at Lowell Memorial Auditorium, had booked a block of rooms for their guests at the UMass Lowell Inn & Conference Center in Downtown Lowell. On Thursday, they found out the reservations had been canceled.