Fix crash when double clicking in packet list area before capturing any packet.

The crash does not happen when using the new packet list.

svn path=/trunk/; revision=32362

gtk/packet_win.c

@@ -131,6 +131,11 @@ void new_window_cb(GtkWidget *w _U_)
   struct PacketWinData *DataPtr;
   int i;
 
+  if (!cfile.current_frame) {
+    /* nothing has been captured so far */
+    return;
+  }
+
 #ifdef NEW_PACKET_LIST
   int err;
   gchar *err_info;