Weird opening of multiple tabs with same filename
When using the `File->Open` option, if the selected file is already open, the editor will just switch to the tab holding this file. However, if you quit the editor with the tab open, then run `aporia filename` the editor will not check previously opened tabs and open a second one. You can quit and rerun with the same command to generate as many cloned tabs as you want.

While the tabs are open the console keeps spewing the following messages:

```
(<unknown>:59891): Gtk-CRITICAL **: gboolean gtk_widget_event(GtkWidget *, GdkEvent *): assertion `WIDGET_REALIZED_FOR_EVENT (widget, event)' failed

(<unknown>:59891): Gdk-CRITICAL **: void gdk_window_invalidate_rect_full(GdkWindow *, const GdkRectangle *, gboolean, ClearBg): assertion `GDK_IS_WINDOW (window)' failed
```
