DngDecoder::decodeData(): really don't allow empty slices/tiles
DngDecoder::decodeData(): really don't allow empty slices/tiles

LebedevRI/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed,darktable-org/rawspeed,LebedevRI/rawspeed