Fix bug in `helm-revive-visible-mark'

[seanirby]

Begin search for candidates to mark revive from the source header string instead of (point-min)

Run the code below with and without my patch to see the difference. Repro steps in the comments.

;; Not a very useful transformer but its just for illustration purposes
(setq xfrmr (lambda (candidates source)
              (helm-get-candidates source)))

(setq source-1 (helm-build-dummy-source "Source 1"
                 :filtered-candidate-transformer (lambda (_c _s)
                                                   (list "5"))
                 :nohighlight t
                 :nomark t))

(setq source-2 (helm-build-sync-source "Source 2"
                 :candidates (mapcar 'prin1-to-string (number-sequence 0 10))
                 :filtered-candidate-transformer xfrmr))

;; Steps to Repro:
;; 1. Run sexp below
;; 2. Select all candidates
;; 3. Enter a character into the prompt
;; 4. Notice how 1 and 5 don't get revived
;; 5. 1 doesn't get revived because it matches the 1 in source-1's header and fails to enter the search loop
;; 6. 5 doesn't get revived because it matches the 5 in source-1's candidate and fails to enter the search loop

;; My PR fixes this behavior because it searches from the sources header rather than (point-min)
(let* ((my-after-update-hook (copy-sequence helm-after-update-hook)))

  (add-hook 'my-after-update-hook (lambda ()
                                          (helm-next-line)))

  (helm :sources `(,source-1 ,source-2)
        :helm-after-update-hook my-after-update-hook))

[thierryvolpiatto]

Thanks merged.