no need for if(tree)

Backported to master-1.12 from master

Change-Id: I5762fb30f57d0f9bc3e5fc786577ed1cc49b64d7
Reviewed-on: https://code.wireshark.org/review/2481
Reviewed-by: Martin Kaiser <wireshark@kaiser.cx>
Reviewed-on: https://code.wireshark.org/review/3002
Reviewed-by: Bill Meier <wmeier@newsguy.com>