color: protect against out-of-bounds reads and writes

color: protect against out-of-bounds reads and writes

want_color_fd() is designed to work only with standard output and
error file descriptors and stores information about each descriptor in
an array. However, it doesn't verify that the passed-in descriptor
lives within that set, which, with a buggy caller, could lead to
access or assignment outside the array bounds.

Signed-off-by: Eric Sunshine <redacted>
Acked-by: Johannes Schindelin <redacted>
Signed-off-by: Jonathan Nieder <redacted>
Signed-off-by: Junio C Hamano <redacted>