(imap4d_copy0): Minor improvement

@@ -93,7 +93,7 @@ imap4d_copy0 (char *arg, int isuid, char *resp, size_t resplen)
 	    {
 	      message_t msg = NULL;
 	      size_t msgno = (isuid) ? uid_to_msgno (set[i]) : set[i];
-	      mailbox_get_message (mbox, msgno, &msg);
+	      if (msgno && mailbox_get_message (mbox, msgno, &msg) == 0)
 		mailbox_append_message (cmbox, msg);
 	    }
 	  mailbox_close (cmbox);

@@ -214,7 +214,9 @@ imap4d_fetch0 (char *arg, int isuid, char *resp, size_t resplen)
 	  util_send (")\r\n");
 	  free (p);
 	}
-      else
+      else if (!isuid)
+	/* According to RFC 3501, "A non-existent unique identifier is
+	   ignored without any error message generated." */
 	{
 	  snprintf (resp, resplen,
 		    "Bogus message set: message number out of range");