Increase `max-specpdl-size' when decoding messages

Some messages (e.g. Outlook automatic replies) need a greater value
than the default one of `max-specpdl-size' to be displayed properly.

mu4e/mu4e-view.el

@@ -371,7 +371,8 @@ article-mode."
       (article-de-base64-unreadable)
       (article-de-quoted-unreadable)
       (run-hooks 'gnus-article-decode-hook)
-      (gnus-article-prepare-display)
+      (let ((max-specpdl-size mu4e-view-max-specpdl-size))
+        (gnus-article-prepare-display))
       (mu4e-view-mode)
       (setq mu4e~view-msg msg)
       (setq gnus-article-decoded-p gnus-article-decode-hook)