Accept indexed images with color values below the first colormap entry (bug #41851). Change made for Matlab compatibility. * ind2gray.m: Change %!tests to accept an indexed image with colors below the first entry in the colormap. * ind2rgb.m: Change %!tests to accept an indexed image with colors below the first entry in the colormap. * ind2x.m: Change input validation to accept all floating point images with integer indices. Issue a warning if any of the indices are below the first entry in the colormap. Map all color indices below the first entry to the first color in the colormap.