[GRASS-git] [OSGeo/grass-addons] 9643db: better error msg

[Markus Neteler]

  Branch: refs/heads/master
  Home:   https://github.com/OSGeo/grass-addons
  Commit: 9643db7643ed964617aa24f76d0021818344770e
      https://github.com/OSGeo/grass-addons/commit/9643db7643ed964617aa24f76d0021818344770e
  Author: Markus Neteler <neteler at gmail.com>
  Date:   2019-09-05 (Thu, 05 Sep 2019)

  Changed paths:
    M grass7/raster/r.learn.ml/r.learn.ml.py

  Log Message:
  -----------
  better error msg