Corrected bug with non-NaN data and calccontour method
Corrected bug with non-NaN data and calccontour method

When adding support for NaNs, one small section of code led to incorrect
color being assigned to lower-than-lowest-contour regions with input data
that didn't include any NaNs and used the calccontour method.  This has
now been fixed.

kakearney/contourfcmap-pkg