* lisp/org-element.el (org-element--cache-sync): Do not check return
value from `org-element--cache-process-request'.
(org-element--cache-process-request): Throw `interrupt' when the
request cannot be processed.
(org-element--cache-process-request): Do not catch interruption from
`org-element--parse-to'.
(org-element--parse-to): Throw `interrupt' when the process stops
before finding the result.