BUG: fix a case when there's only a single building to be passed to voronoi_frames

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.0%. Comparing base (4037c70) to head (b7b11fd). Report is 56 commits behind head on main.

Additional details and impacted files

[](https://app.codecov.io/gh/pysal/momepy/pull/621?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pysal) ```diff @@ Coverage Diff @@ ## main #621 +/- ## ======================================= + Coverage 97.4% 98.0% +0.6% ======================================= Files 26 38 +12 Lines 4328 6176 +1848 ======================================= + Hits 4214 6051 +1837 - Misses 114 125 +11 ``` | [Files](https://app.codecov.io/gh/pysal/momepy/pull/621?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pysal) | Coverage Δ | | |---|---|---| | [momepy/functional/\_elements.py](https://app.codecov.io/gh/pysal/momepy/pull/621?src=pr&el=tree&filepath=momepy%2Ffunctional%2F_elements.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pysal#diff-bW9tZXB5L2Z1bmN0aW9uYWwvX2VsZW1lbnRzLnB5) | `99.1% <100.0%> (ø)` | | | [momepy/functional/tests/test\_elements.py](https://app.codecov.io/gh/pysal/momepy/pull/621?src=pr&el=tree&filepath=momepy%2Ffunctional%2Ftests%2Ftest_elements.py&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=pysal#diff-bW9tZXB5L2Z1bmN0aW9uYWwvdGVzdHMvdGVzdF9lbGVtZW50cy5weQ==) | `99.0% <100.0%> (ø)` | |