Free one more allocated callback data in TextWindow. This is needed
because text_win_close_cb() is also doing the same as TextWindow__gc().
Bug: 16177
Change-Id: I7c2211e154a6db1dccd22df824e76cce575040c9
Reviewed-on: https://code.wireshark.org/review/34990
Petri-Dish: Stig Bjørlykke <stig@bjorlykke.org>
Tested-by: Petri Dish Buildbot
Reviewed-by: Stig Bjørlykke <stig@bjorlykke.org>