wxGUI/animation: set default export file type choice option (#838)

gui/wxpython/animation/dialogs.py

@@ -1189,6 +1189,7 @@ class ExportDialog(wx.Dialog):
         choices = [_("image sequence"), _("animated GIF"), _("SWF"), _("AVI")]
         self.formatChoice = wx.Choice(parent=panel, id=wx.ID_ANY,
                                       choices=choices)
+        self.formatChoice.SetSelection(0)
         self.formatChoice.Bind(
             wx.EVT_CHOICE,
             lambda event: self.ChangeFormat(