Do not set zero bits and add features.

screen-write.c

@@ -1407,6 +1407,7 @@ screen_write_sync_redraw_cb(const struct tty_ctx *ttyctx, u_int py, u_int ny)
 {
 	struct window_pane	*wp = ttyctx->arg;
 
+	if (ny != 0)
 		bit_nset(wp->sync_dirty, py, py + ny - 1);
 }
 

tty-features.c

@@ -668,6 +668,7 @@ tty_default_features(struct client *c, const char *name, u_int version)
 			      "cstyle,"
 			      "extkeys,"
 			      "focus,"
+			      "imagescroll,"
 			      "margins,"
 			      "overline,"
 			      "hyperlinks,"
@@ -684,6 +685,7 @@ tty_default_features(struct client *c, const char *name, u_int version)
 			      "extkeys,"
 			      "focus,"
 			      "hyperlinks,"
+			      "imagescroll,"
 			      "osc7,"
 			      "sync,"
 			      "usstyle,"

tty.c

@@ -288,6 +288,10 @@ tty_open(struct tty *tty, char **cause)
 	}
 	tty->flags |= TTY_OPENED;
 
+#ifdef ENABLE_IMAGES
+	image_tty_update(tty);
+#endif
+
 	tty->flags &= ~(TTY_NOCURSOR|TTY_FREEZE|TTY_BLOCK|TTY_TIMER);
 
 	event_set(&tty->event_in, c->fd, EV_PERSIST|EV_READ,