Ignore errors if display-buffer ALIST is malformed

The gud.el library uses display-buffer incorrectly, by passing a list of
functions as its second argument, instead of as a nested list.

CORRECT:
  (display-buffer buffer
    '((display-buffer-reuse-window
       display-buffer-in-previous-window
       display-buffer-same-window display-buffer-pop-up-window)))

INCORRECT (how gud does it):
  (display-buffer buffer
    '(display-buffer-reuse-window
      display-buffer-in-previous-window
      display-buffer-same-window display-buffer-pop-up-window))

This causes "wrong-type-argument: listp
display-buffer-in-previous-window" error. However, it appears Emacs
handles malformed alists by just ignoring them, so Doom will do the
same.

Reported by @maskray

modules/ui/popup/autoload/popup.el

@@ -99,12 +99,12 @@ and enables `+popup-buffer-mode'."
     (let ((alist  ; handle defaults
            (cl-remove-duplicates
             (append alist +popup-default-alist)
-            :key #'car :from-end t))
+            :key #'car-safe :from-end t))
           (parameters
            (cl-remove-duplicates
             (append (cdr (assq 'window-parameters alist))
                     +popup-default-parameters)
-            :key #'car :from-end t)))
+            :key #'car-safe :from-end t)))
       ;; handle `size'
       (when-let* ((size  (cdr (assq 'size alist)))
                   (side  (or (cdr (assq 'side alist)) 'bottom))