Fix Bug#26127

Fix Bug#26127

* lisp/filenotify.el (file-notify--rm-descriptor): Check, that
there is a function which could be called.  (Bug#26127)

* test/lisp/filenotify-tests.el (file-notify--test-cleanup):
Clear also `file-notify-descriptors'.
(file-notify--test-make-temp-name): Move up.
(file-notify-test02-rm-watch): New test.
(file-notify-test03-events, file-notify-test04-autorevert)
(file-notify-test05-file-validity)
(file-notify-test06-dir-validity)
(file-notify-test07-many-events, file-notify-test08-backup)
(file-notify-test09-watched-file-in-watched-dir)
(file-notify-test10-sufficient-resources): Rename.