these two vars are initialized to NULL,
we don't have to set them to NULL again

Change-Id: Iacd01ca207d2b74ebdbd5a7635f00e6d03b13721
Reviewed-on: https://code.wireshark.org/review/3726
Reviewed-by: Martin Kaiser <wireshark@kaiser.cx>
Tested-by: Martin Kaiser <wireshark@kaiser.cx>