Fixing Windows `patch_cmd` setup helper to exit gracefully.
Fixing Windows `patch_cmd` setup helper to exit gracefully.

Was failing with an AttributeError when the Fortran compiler
could not be located.

See:
https://ci.appveyor.com/project/dhermes/bezier/build/1.0.543.master/job/jnkiu7b6ywsacvd5

dhermes/bezier,dhermes/bezier,dhermes/bezier