Error when using PCE mode native palettes to generate tiles.

[est77]

Repro case:

superfamiconv palette -i tileset.png -M pce -0 000000 -d tiles.pal -v
superfamiconv tiles -i tileset.png -p tiles.pal -d tiles.chr -o tiles_chr.png -M pce -v

Error: No matching palette for tile at 16,0 in source image

Using json palettes instead of native palettes seems to work ok.