mu4e: fix some warnings on older emacsen

mu4e/mu4e-message.el

@@ -215,8 +215,11 @@ If MSG is nil, use `mu4e-message-at-point'."
     (when-let ((msg (mu4e-message-at-point 'noerror)))
       (when (buffer-live-p mu4e--sexp-buffer-name)
         (kill-buffer mu4e--sexp-buffer-name))
-      (with-current-buffer-window (get-buffer-create mu4e--sexp-buffer-name) nil nil
-        (lisp-data-mode)
+      (with-current-buffer-window
+          (get-buffer-create mu4e--sexp-buffer-name) nil nil
+        (if (fboundp 'lisp-data-mode)
+            (lisp-data-mode)
+          (lisp-mode))
         (insert (pp-to-string msg))
         (font-lock-ensure)
         ;; add basic `quit-window' bindings

mu4e/mu4e-notification.el

@@ -84,7 +84,7 @@ support."
              ;;              "gnus/gnus.png"))
              :actions '("Show" "Favorite bookmark"
                         "default" "Favorite bookmark")
-             :on-action (lambda (_ _) (mu4e-jump-to-favorite)))))
+             :on-action (lambda (_1 _2) (mu4e-jump-to-favorite)))))
      ;; ... TBI: other notifications ...
      (t ;; last resort
       (mu4e-message "%s: %s" title body)))))

mu4e/mu4e-search.el

@@ -392,7 +392,7 @@ status, STATUS."
    ((looking-back "mime:\\([a-zA-Z0-9/-]*\\)" nil)
     (list (match-beginning 1)
           (match-end 1)
-          (mailcap-mime-types)))
+          (when (fboundp 'mailcap-mime-types) (mailcap-mime-types))))
    ((looking-back "\\(from\\|to\\|cc\\|bcc\\|contact\\|recip\\):\\([a-zA-Z0-9/.@]*\\)" nil)
     (list (match-beginning 2)
           (match-end 2)

mu4e/mu4e-view.el

@@ -640,8 +640,7 @@ As a side-effect, a message that is being viewed loses its
         ;; problems later (#2260, #2508), so let's remove those
         (article-remove-cr)
         (setq-local mu4e--view-message msg)
-        (mu4e--view-render-buffer msg)
-        (setq-local mu4e--view-mime-part-cached nil))
+        (mu4e--view-render-buffer msg))
       (mu4e-loading-mode 0)))
   (unless (mu4e--view-detached-p gnus-article-buffer)
     (with-current-buffer mu4e-linked-headers-buffer