[Bug]: org-capture-place-plain-text error when template :unnarrowed

[No Wayman]

org-capture-place-plain-text throws an error for templates which 
meet the following criteria:
 - entry type is 'plain
 - the template has a non-nil :unnarrowed option
 - the template string is not empty and does not explicitly 
 include "%?"

Seems to be thrown in this section of 
org-capture-place-plain-text:
 #+begin_src emacs-lisp
        (when (or (search-backward "%?" beg t)
                  (search-forward "%?" end t))
 #+end_src

A minimal failing case:
#+begin_src emacs-lisp
(let ((org-capture-templates
      '(("t" "test" plain (file "/tmp/bug.org")
         "FAIL" :unnarrowed t))))
 (org-capture nil "t"))
#+end_src

And a minimal passing case:
#+begin_src emacs-lisp
(let ((org-capture-templates
      '(("t" "test" plain (file "/tmp/bug.org")
         "PASS%?" :unnarrowed t))))
 (org-capture nil "t"))
#+end_src