[Magick-bugs] bit depth of 4bit Gif file

[duc.sequere.aut.de.via.decede at imagemagick.org]

> Actually it is detected as a 8bit file.

The image has 16 colors but the colormap requires 8-bits to encode the
colors.  If the colors RGB values ranged from 0 to 15, ImageMagick would
report a depth of 4.

  Colors: 16
    0: (255,255,255)      grey100
    1: (232,232,232)      grey91
    2: (208,208,208)      #D0D0D0
    3: (192,192,192)      silver
    4: (176,176,176)      grey69
    5: (168,168,168)      grey66
    6: (152,152,152)      #989898
    7: (136,136,136)      #888888
    8: (112,112,112)      grey44
    9: ( 96, 96, 96)      #606060
    10: ( 72, 72, 72)     #484848
    11: ( 48, 48, 48)     grey19
    12: ( 40, 40, 40)     #282828
    13: ( 32, 32, 32)     #202020
    14: (  8,  8,  8)     grey3
    15: (  0,  0,  0)     black