utils: get_compacted_slices: fix issue if urls are empty

2 jobs for payno-master-patch-46245 in 35 seconds (queued for 1 second)
Name Stage Failure
failed
linux_shell Test
Collecting appdirs>=1.4.0
Using cached appdirs-1.4.4-py2.py3-none-any.whl (9.6 kB)
Requirement already satisfied: numpy>=1.2.0 in /dev/shm/gitlab_ci/nabu/venv/lib/python3.8/site-packages (from scikit-cuda) (1.22.1)
Collecting MarkupSafe>=0.9.2
Using cached MarkupSafe-2.0.1-cp38-cp38-manylinux_2_5_x86_64.manylinux1_x86_64.manylinux_2_12_x86_64.manylinux2010_x86_64.whl (30 kB)
Installing collected packages: MarkupSafe, appdirs, pytools, mako, pycuda, scikit-cuda
Successfully installed MarkupSafe-2.0.1 appdirs-1.4.4 mako-1.1.6 pycuda-2021.1 pytools-2021.2.9 scikit-cuda-0.5.3
$ bash .gitlab/get_version_diff.sh
Please update the micro version number. Current version on master branch is "2021.2.1-rc2"
failed
linux_docker Test
  Downloading scipy-1.7.3-cp37-cp37m-manylinux_2_12_x86_64.manylinux2010_x86_64.whl (38.1 MB)
Requirement already satisfied: numpy<1.23.0,>=1.16.5 in /root/gitlab_ci/nabu/venv/lib/python3.7/site-packages (from scipy) (1.21.5)
Installing collected packages: scipy
Successfully installed scipy-1.7.3
$ if [[ $CI_RUNNER_TAGS == *"gpu"* ]]; then pip install pycuda scikit-cuda; fi
$ bash .gitlab/get_version_diff.sh
Please update the micro version number. Current version on master branch is "2021.2.1-rc2"
Cleaning up file based variables
ERROR: Job failed: exit code 1