tiff: Avoid limiting palette colors to 8 bits.
tiff: Avoid limiting palette colors to 8 bits.

Previously fz_unpack_tile() could not handle >8 bit images,
so palettized tiff colors had to be limited to 8 bits.
Now when fz_unpack_tile() does handles >8 bit images do not
limit the samples in the colormap to 8 bits.

This fixes Coverity CID 150612.

sebras/mupdf,sebras/mupdf,sebras/mupdf,ArtifexSoftware/mupdf,TamirEvan/mupdf,sebras/mupdf,ArtifexSoftware/mupdf,TamirEvan/mupdf,TamirEvan/mupdf,ccxvii/mupdf,ArtifexSoftware/mupdf,ccxvii/mupdf,ArtifexSoftware/mupdf,sebras/mupdf,TamirEvan/mupdf,TamirEvan/mupdf,ArtifexSoftware/mupdf,ArtifexSoftware/mupdf,sebras/mupdf,TamirEvan/mupdf,ArtifexSoftware/mupdf,ccxvii/mupdf,TamirEvan/mupdf,ArtifexSoftware/mupdf,ccxvii/mupdf,ccxvii/mupdf,TamirEvan/mupdf,ccxvii/mupdf