Logcat: Fix crashes when try to use logcat_text open routine on binary file

Change-Id: Ied0778af9d5ff0e49c6efd4ea9411ae1a72cb8e5
Reviewed-on: https://code.wireshark.org/review/4190
Petri-Dish: Michal Labedzki <michal.labedzki@tieto.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>