Fix folder creation error (Bug#67361)

* lisp/mh-e/mh-funcs.el (mh-kill-folder), lisp/mh-e/mh-search.el
  (mh-index-new-folder), lisp/mh-e/mh-utils.el (mh-prompt-for-folder):
  Check for existence of speedbar-buffer rather than
  mh-speed-folder-map. The latter can exist if mh-speed has only been
  loaded but not displayed.

lisp/mh-e/mh-funcs.el

@@ -108,7 +108,7 @@ folder. This is useful for folders that are easily regenerated."
             (window-config mh-previous-window-config))
         (mh-set-folder-modified-p t)    ; lock folder to kill it
         (mh-exec-cmd-daemon "rmf" 'mh-rmf-daemon folder)
-        (when (boundp 'mh-speed-folder-map)
+        (when (and (boundp 'speedbar-buffer) speedbar-buffer)
           (mh-speed-invalidate-map folder))
         (mh-remove-from-sub-folders-cache folder)
         (mh-set-folder-modified-p nil)  ; so kill-buffer doesn't complain

lisp/mh-e/mh-search.el

@@ -1569,7 +1569,7 @@ If the folder returned doesn't exist then it is created."
     (save-excursion (mh-exec-cmd-quiet nil "rmf" chosen-name))
     (mh-exec-cmd-quiet nil "folder" "-create" "-fast" chosen-name)
     (mh-remove-from-sub-folders-cache chosen-name)
-    (when (boundp 'mh-speed-folder-map)
+    (when (and (boundp 'speedbar-buffer) speedbar-buffer)
       (mh-speed-add-folder chosen-name))
     chosen-name))
 

lisp/mh-e/mh-utils.el

@@ -795,7 +795,7 @@ used in searching."
              (message "Creating %s" folder-name)
              (mh-exec-cmd-error nil "folder" folder-name)
              (mh-remove-from-sub-folders-cache folder-name)
-             (when (boundp 'mh-speed-folder-map)
+             (when (and (boundp 'speedbar-buffer) speedbar-buffer)
                (mh-speed-add-folder folder-name))
              (message "Creating %s...done" folder-name))
             (new-file-flag