Crash when "gray" CPT is used

[ZMAlt]

Hi, @joa-quim

I found a weird crash when "gray" CPT is used.

using GMT
grd = grdcut("@earth_relief_01d", region = (110, 120, 10, 20))
cpt = grd2cpt(grd, C = "gray")  # same situation for makecpt
grdimage(grd, C = cpt, savefig = "test.pdf")

If "gray" is replaced with other cpt, there is no crash.

[joa-quim]

Confirm it too. Thanks.

[joa-quim]

This is due to a bug in GMT that returns a conflicting info for the gray.cpt master CPT. Fixed in master by testing if the colors are gray or not.

[ZMAlt]

Great.
I have tested it using the master branch. It works now.
Thank you.