Describe the bug
A clear and concise description of what the bug is:
flopy.utils.cvfdutil.shapefile_to_cvfd fails when skip_hanging_node_check = True
because vertexdict_keys is not defined

To Reproduce
use
flopy.utils.cvfdutil.shapefile_to_cvfd(shp, skip_hanging_node_check = True)
or
flopy.utils.cvfdutil.to_cvfd( ... , skip_hanging_node_check = True)

Expected behavior
for meshes different from quadtree grids the use of ' skip_hanging_node_check = True ' should be allowed
currently vertexdict_keys = list(vertexdict.keys()) is defined inside this check: if not skip_hanging_node_check.
vertexdict_keys should be defined outside that IF.

Additional context
I was trying to convert a Voronoi mesh shapefile created through geopandas, but the hanging_node_check got stuck and ran forever. Then I tried to skip the check and found that problem. In theory, the bug is straightforward to fix ( I did it on my local version), but I still wonder if there may be something wrong with my mesh that makes the test last forever. any thoughts about it are welcome
Cheers