Clearing the screen while drawing the first object, e.g. button.

[Metal-codes]

While creating the menu, I encountered an error where the text created before the button is cleared on the display.

Steps to reproduce:

1. Add a call to the method ui->drawString(...).
2. Add a call to the method ui->draw(btn, ...).

Expected Behavior: The text added before the button should be displayed on the screen.

Actual Behavior: The text added before the button is cleared from the screen.

System information:

• FireBeetle 2 ESP32-E (DFR0654-F)
• Fermion: 3.5” 480x320 TFT LCD (DFR0669)
• PlatformIO

Questions:

1. What is the purpose of this code?
2. This fragment of code is necessary?

The code fragment responsible for this logic: https://github.com/DFRobot/DFRobot_GDL/blob/8b22fa9b69ffb3e455fc0212300110c06da76ff4/src/DFRobot_UI.cpp#L350-L354