org-ql-view-buffer applies agenda-filter-preset from previous (unrelated) agenda-view

Precondition:
I invoke a normal agenda-view (custom-command) with `org-agenda-tag-filter-preset` set.

bug:
any `org-ql-search` invocation applies the filter-preset from the normal agenda-view to its own buffer. the only way to get rid of the filter-preset is to invoke a normal agenda command that has no filter-preset and then call `org-ql-search`.

Hints to a possible fix:
if i alter the definition of `org-ql-view--display` so that `(org-agenda-prepare)` is called inside the view-buffer, the filter-preset does not carry over (sorry, no pull request):
> .....
> (with-current-buffer buffer
> (org-agenda-prepare) ;; call this here to prepare filter-settings for org-agenda-finalize later
> (use-local-map org-ql-view-map)
> ;; Prepare buffer, saving data for refreshing.
> (cl-loop for symbol in vars
> ....

From what i see, the call to `org-agenda-prepare` is necessary for `org-agenda-finalize` to do the right thing. I didnt check for any side-effects of this change though (first time digging this deep ;-)