[mu4e bug] thread folding hides the next unrelated message in headers view about mu HOT 2 CLOSED

looks like an off-by-one error when determining the boundary between the thread to fold and the next thread. This change fixed it for me, but I haven't had a chance to look over the implications outside of the fix:

(defun mu4e-thread-next()
  "Get the root of the next thread (if any)."
  (save-excursion
    (when (mu4e-thread-goto-next)
      (1- (mu4e-thread-root)))))

from mu.

Fixed in master.

from mu.