bta_jv_act: Avoid potential NULL dereference

When 'tc' is NULL (a condition we check for), 't' is never
set to a non-NULL value, yet is still dereferenced.  We move
our NULL check of 't' to make this code safe.

Test: TreeHugger
Change-Id: Ibfea74963dd763401ea18ccdd24a51ecd0baefc5