v.surf.idw: less confusing error message

[neteler]

The current error message of v.surf.idw is unhelpful and misleading (see https://lists.osgeo.org/pipermail/grass-user/2021-February/082209.html).

GRASS :Coal-Test-Shapefile > v.surf.idw input=coal_test output=coal_test_tested
Input vector map <coal_test@PERMANENT> is 2D - using categories to
interpolate
0 points loaded
ERROR: No points found

The reason here is simply that the computation region does not match that of the vector map.

GRASS RD_83_GK5/PERMANENT:Coal-Test-Shapefile > v.surf.idw input=coal_test output=coal_test_tested --o
Input vector map <coal_test@PERMANENT> is 2D - using categories to
interpolate
0 points loaded
ERROR: No points found. Check current region with g.region

Other candidates in this regard:

v.neighbors/main.c
416:        G_warning(_("No points found"));

v.normal/main.c
195:	G_fatal_error(_("No points found"));