Bluetooth: Fix some Clang Analyzer warnings

Logic error Dereference of null pointer epan/dissectors/packet-bthci_acl.c 379
Logic error Dereference of null pointer epan/dissectors/packet-bthci_acl.c 390
Logic error Dereference of null pointer epan/dissectors/packet-btsdp.c 3673
Logic error Dereference of null pointer epan/dissectors/packet-btsdp.c 1439
Logic error Dereference of null pointer epan/dissectors/packet-btsdp.c 1662

Thanks for Alexis La Goutte for pointing that.

Change-Id: Ia646b33de9e368d32983efddfaa41edf7896d7fd
Reviewed-on: https://code.wireshark.org/review/4165
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>