Fix imenu with Clojure code in string or comment

Ignore error that's thrown from `down-list` when called
with point inside a string or comment.

E.g. with code like:

```
(defn foo []
  (let [a "
(defn b [_]
  (bar {:bla \"bla\"}))"]))
```

`clojure-match-next-def` calls `down-list` with point inside
the string and `down-list` will throw an user-error with
"This command doesn't work in strings or comments".

This user-error in `down-list` got introduced 2022-05-06
with https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=0b3b295776ce723885c9997ab26d57314db2a5df

The `when ignore-errors` could be replaced with
`unless (ppss-comment-or-string-start (syntax-ppss))`
once the minimum requirement for clojure-mode is Emacs 27.

CHANGELOG.md

@@ -10,6 +10,7 @@
 
 * [#581](https://github.com/clojure-emacs/clojure-mode/issues/581): Fix font locking not working for keywords starting with a number.
 * [#377](https://github.com/clojure-emacs/clojure-mode/issues/377): Fix everything starting with the prefix 'def' being highlighted as a definition form. Now definition forms are enumerated explicitly in the font-locking code, like all other forms.
+* [#638](https://github.com/clojure-emacs/clojure-mode/pull/638): Fix imenu with Clojure code in string or comment.
 
 ## 5.15.1 (2022-07-30)
 

clojure-mode.el

@@ -776,7 +776,9 @@ Called by `imenu--generic-function'."
       (let (found?
             (deftype (match-string 2))
             (start (point)))
-        (down-list)
+        ;; ignore user-error from down-list when called from inside a string or comment
+        (ignore-errors
+          (down-list))
         (forward-sexp)
         (while (not found?)
           (ignore-errors