* mu4e-view.el: make sure the output buffer is writable

emacs/mu4e-view.el

@@ -685,10 +685,11 @@ attachments) in response to a (mu4e-proc-extract 'temp ... )."
 	  (concat param " " path)))
       ((string= what "pipe")
 	;; 'param' will be the pipe command, path the infile for this
-	(switch-to-buffer (get-buffer-create "*mu4e-output*"))
-	(erase-buffer)
-	(call-process-shell-command param path t t)
-	(view-mode))
+	(let ((inhibit-read-only t))
+	  (switch-to-buffer (get-buffer-create "*mu4e-output*"))
+	  (erase-buffer)
+	  (call-process-shell-command param path t t)
+	  (view-mode)))
       ((string= what "emacs")
 	(find-file path))
       (t (error "Unsupported action %S" what))))