Unhide cursor on RIS (\033c)

It is unclear if it's "required" to do this on RIS, but it's useful when
calling reset(1) after interactive programs have crashed and garbled up
the screen.

FWIW, other terminals do it as well (tested with XTerm, VTE, Kitty,
Alacritty, Linux VT).

st.c

@@ -2330,6 +2330,7 @@ eschandle(uchar ascii)
 		treset();
 		resettitle();
 		xloadcols();
+		xsetmode(0, MODE_HIDE);
 		break;
 	case '=': /* DECPAM -- Application keypad */
 		xsetmode(1, MODE_APPKEYPAD);