(smtpmail-send-it): Use convert-standard-filename to make file names

for queued mail safe on Windows (`:' is invalid in file names on
Windows).

lisp/mail/smtpmail.el

@@ -238,7 +238,8 @@ This is relative to `smtpmail-queue-dir'.")
 			       smtpmail-queue-dir
 			       (concat (time-stamp-yyyy-mm-dd)
 				       "_" (time-stamp-hh:mm:ss))))
-		   (file-elisp (concat file-data ".el"))
+		      (file-data (convert-standard-filename file-data))
+		      (file-elisp (concat file-data ".el"))
 		   (buffer-data (create-file-buffer file-data))
 		   (buffer-elisp (create-file-buffer file-elisp))
 		   (buffer-scratch "*queue-mail*"))