Endpoint: wrong filter when select a UDP endpoint (INVALID == a.x.y.z ...)

Change-Id: Ie46d6c201df0b0164a8bf96c02d6430734fd2948
Reviewed-on: https://code.wireshark.org/review/5518
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>