drm_touchtest: fix visual bugs
Current version of touch screen test does not work reliably:
- test boxes sometimes do not appear on screen at all;
- or previous test boxes remain on screen after being clicked.
These problems are caused by timer handler, which is triggered during a screen transition. At this moment, the handler interrupts the main drawing loop to redraw a timer in the center of the screen.
Add an internal variable to keep the current state of the application and, if refresh_screen() is active, do not refresh the timer.
Edited by Dmitry Petrov