Fix memory error in UT tracking

When running the master branch with cuda-memcheck errors occur from calculate_windows(...) and ut_search_windows(...), see for example this log:

https://ybin.me/p/99009f4f56e3910f#Acuzl+d+UqlMzXcyB/u9d/FlkNz3r9P0X0E4DGZcGUo=

@plfernan could you please take a look?