openSAFETY: Adapt CRC for false-positives

 - There are rare false-positives, where the entire
   frame consists of 0 except the addr and id field,
   which will lead to a correct crc#1 calculation,
   but still to a false-positive detection. This
   patch fixes that

 - Two undefinite-loop errors are corrected as well

Change-Id: Ibe5e56e0172ad3a3046bdc024da3711987116e8e
Reviewed-on: https://code.wireshark.org/review/3918
Reviewed-by: Roland Knall <rknall@gmail.com>
Petri-Dish: Pascal Quantin <pascal.quantin@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>
(cherry picked from commit db6f197c962200e0be717b953c0ebe7d7c908bf1)
Reviewed-on: https://code.wireshark.org/review/3950
Reviewed-by: Michael Mann <mmann78@netscape.net>