fixup! core-jump: fixed a typo

This commit prevents the error when `handler` is atomic instead of a list.

core/core-jump.el

@@ -77,7 +77,7 @@ They are in order: `spacemacs-jump-handlers',
           (old-point (point)))
       (dolist (-handler (spacemacs//get-jump-handlers))
         (let* ((handler (if (listp -handler) (car -handler) -handler))
-               (async (plist-get (cdr handler) :async)))
+               (async (plist-get (cdr-safe handler) :async)))
           (ignore-errors
             (call-interactively handler))
           (when (or (eq async t)