Eat up "CSI 58" sequences

This is used in the wild by systemd systemctl for example and st
misinterpreted it as "blink", because it didn't know "58", then saw "5"
as "blink", and then didn't know "245".

This should print "foo" as normal text:

    printf '\e[58:5:245mfoo\n'
    printf '\e[58:2:50:100:200mfoo\n'

1 files changed, 6 insertions, 0 deletions

diff --git a/st.c b/st.c
index 03b9bc8..37f38c5 100644
--- a/st.c
+++ b/st.c
@@ -1430,6 +1430,12 @@ tsetattr(const int *attr, int l)
                 case 49:
                         term.c.attr.bg = defaultbg;
                         break;
+                case 58:
+                        /* This starts a sequence to change the color of
+                         * "underline" pixels. We don't support that and
+                         * instead eat up a following "5;n" or "2;r;g;b". */
+                        tdefcolor(attr, &i, l);
+                        break;
                 default:
                         if (BETWEEN(attr[i], 30, 37)) {
                                 term.c.attr.fg = attr[i] - 30;