Fix crash on resume in vt(9).

Statically allocated terminal window have not initialized callout handler, so we
have to initialize it even for existing window if it is console window.

Reported by:	gjb and many
Tested by:	gjb
MFC after:	7 days
Sponsored by:	The FreeBSD Foundation

sys/dev/vt/vt_core.c

@@ -1872,6 +1872,9 @@ vt_upgrade(struct vt_device *vd)
 		if (vw == NULL) {
 			/* New window. */
 			vw = vt_allocate_window(vd, i);
+		} else if (vw->vw_flags & VWF_CONSOLE) {
+			/* For existing console window. */
+			callout_init(&vw->vw_proc_dead_timer, 0);
 		}
 		if (i == VT_CONSWINDOW) {
 			/* Console window. */