Initialize context property in alignment test handler function.

screen-write.c

@@ -775,6 +775,8 @@ screen_write_alignmenttest(struct screen_write_ctx *ctx)
 	s->rupper = 0;
 	s->rlower = screen_size_y(s) - 1;
 
+	screen_write_initctx(ctx, &ttyctx);
+
 	screen_write_collect_clear(ctx, 0, screen_size_y(s) - 1);
 	tty_write(tty_cmd_alignmenttest, &ttyctx);
 }