XFree colormap_ret and initialize it when appropriate.

Variable "colormap_ret" goes out of scope
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Signed-off-by: Erkki Seppälä <erkki.seppala@vincit.fi>
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Backported-to-NX-by: Ulrich Sibiller <uli42@gmx.de>