Fix error related to buffer-names introduced by (#934).

* helm-buffers.el (helm-buffers--quote-truncated-buffer,
helm-buffer--get-preselection): Transform argument in buffer-name.

helm-buffers.el

@@ -361,18 +361,19 @@ Should be called after others transformers i.e (boring buffers)."
                         name)
                       (get-buffer i))))
 
-(defun helm-buffer--get-preselection (buffer-name)
-  (concat "^"
-          (if (and (null helm-buffer-details-flag)
-                   (numberp helm-buffer-max-length)
-                   (> (string-width buffer-name)
-                      helm-buffer-max-length))
-              (regexp-quote
-               (helm-substring-by-width
-                buffer-name helm-buffer-max-length))
-            (concat (regexp-quote buffer-name)
-                    (if helm-buffer-details-flag
-                        "$" "[[:blank:]]+")))))
+(defun helm-buffer--get-preselection (buffer)
+  (let ((bufname (buffer-name buffer)))
+    (concat "^"
+            (if (and (null helm-buffer-details-flag)
+                     (numberp helm-buffer-max-length)
+                     (> (string-width bufname)
+                        helm-buffer-max-length))
+                (regexp-quote
+                 (helm-substring-by-width
+                  bufname helm-buffer-max-length))
+                (concat (regexp-quote bufname)
+                        (if helm-buffer-details-flag
+                            "$" "[[:blank:]]+"))))))
 
 (defun helm-toggle-buffers-details ()
   (interactive)
@@ -683,13 +684,14 @@ If REGEXP-FLAG is given use `query-replace-regexp'."
   (with-helm-temp-hook 'helm-after-persistent-action-hook
     (helm-force-update (regexp-quote (helm-get-selection nil t)))))
 
-(defun helm-buffers--quote-truncated-buffer (bufname)
-  (regexp-quote
-   (if helm-buffer-max-length
-       (helm-substring-by-width
-        bufname helm-buffer-max-length
-        "")
-     bufname)))
+(defun helm-buffers--quote-truncated-buffer (buffer)
+  (let ((bufname (buffer-name buffer)))
+    (regexp-quote
+     (if helm-buffer-max-length
+         (helm-substring-by-width
+          bufname helm-buffer-max-length
+          "")
+         bufname))))
 
 (defun helm-buffers-persistent-kill (_buffer)
   (let ((marked (helm-marked-candidates)))