[thredds] Bug fix for WMS/WCS on stable release 4.1 for TDS

TDS 4.1.5 is now available from the TDS page:

http://www.unidata.ucar.edu/projects/THREDDS/tech/TDS.html

This release fixes a bug handling missing values in WMS and WCS. If you are 
running those services, we recommend that you upgrade.

More details available in the CHANGES.txt file:

ftp://ftp.unidata.ucar.edu/pub/thredds/4.1/CHANGES.txt