[raster] Band index in rt_core functions must be 0-based

[jorgearevalo]

Most of the functions that receive as argument a band index in rt_core expect 0-based index. But function "rt_raster_dump_as_wktpolygons" expects a 1-based index, and MapAlgebra? (under construction) too. All the core functions should follow the same principles. The easier way is to ensure all the functions follow the 0-based scheme

[dustymugs]

rt_raster_has_no_band() also is using a 1-based index. There are no mapalgebra functions in rt_core so that isn't a problem.

[dustymugs]

Standardized 0-based index for band number to rt_raster_dump_as_wktpolygons() in r7997.

[dustymugs]

Changed rt_raster_has_no_band() to be 0-based in r7998. There are no more functions within rt_core/* that do not use 0-based band indices.