RGBGFX `makePalsAsSpecified` does not account for transparent pixels

[Rangi42]

Here's t1.png, all #0000FF with one transparent pixel:

./rgbgfx -c "#0000FF,#FF0000" -o t1.2bpp -p t1.pal t1.png
error: Failed to fit tile colors [GB:00,00,31] in specified palettes
note: The following palette was specified:
      - [GB:31,00,00]
Conversion aborted after 1 error

$ ./rgbgfx -c "#0000FF,#FF0000,#FF00FF,#FFFFFF" -o t1.2bpp -p t1.pal t1.png
error: Failed to fit tile colors [GB:00,00,31] in specified palettes
note: The following palette was specified:
      - [GB:31,00,00; GB:31,00,31; GB:31,31,31]
Conversion aborted after 1 error

And here's t2.png, all #FF0000 with one transparent pixel:

$ ./rgbgfx -c "#0000FF,#FF0000" -o t2.2bpp -p t2.pal t2.png
$ ./rgbgfx -c "#0000FF,#FF0000" -o t2.2bpp -p t2.pal -r 1 t2-rev.png
warning: Colors in the palette file do not match those specified with '-c'
Colors specified in the palette file:         ...versus with '-c':
[#0000ffff, #ff0000ff, #ffffff00, #ffffff00]  [#0000ffff, #ff0000ff, <none>   , <none>   ]

$ ./rgbgfx -c "#0000FF,#FF0000,#FF00FF,#FFFFFF" -o t2.2bpp -p t2.pal t2.png
$ ./rgbgfx -c "#0000FF,#FF0000,#FF00FF,#FFFFFF" -o t2.2bpp -p t2.pal -r 1 t2-rev.png
$ img2sixel t2-rev.png

[Rangi42]

The indented correct behavior, from the manual:

First, if the image contains any transparent pixel, color #0 of all palettes will be allocated to it. This is done even if palettes were explicitly specified using -c; then the specification only covers color #1 onwards. (If you do not want this, ask your image editor to remove the alpha channel.)

So specifying three or fewer colors with -c for t1.png or t2.png should work, and put transparent as color #0; and specifying four colors should fail with "error: Each palette can only contain up to 3 colors".