Adjust error message for a bookmark that doesn't change the buffer

1. Activities was unable to get a buffer for bookmark:

(#("Activity: DC-13 " 0 16 (bmkp-full-record (#1 (time 26058 30868 176769 395000) (visits . 0) (activities-name . "DC-13 ") (handler . activities-bookmark-handler)))) (filename . " - no file -") (buffer-name . "*Ibuffer*") (front-context-string . " MRL Name ") (rear-context-string) (front-context-region-string) (rear-context-region-string) (visits . 1) (time 26058 31089 378453 71000) (created 26058 30967 111331 208000) (position . 1))

It's likely that the bookmark's file no longer exists, in which case you may need to relocate it and redefine this activity.

If this is not the case, please report this error to the `activities' maintainer.

from the "bookmarks" file -- it is there:
(#1=(#("Activity: DC-13 " 0 16
(bmkp-full-record #1#))
(time 26058 30868 176769 395000)
(visits . 0)
(activities-name . "DC-13 ")
(handler . activities-bookmark-handler))

2. For other activities, no bookmark was automaticically created