e-paper busy endless loop work-around for epd7in5_V2.py

[tkameroski]

This updates epd7in5_V2.py to create a break in the ReadBusy loop if it becomes endless. I have had problems with it entering the while loop and never exiting on my Pi Zero W. With this change, it breaks the loop and allows the program to keep running instead of freezing. I have had the loop become endless relatively frequently on the Pi0W and much less often on a Pi 3 and a Pi 4b. This change is taken from the work of others trying to solve issue https://github.com/waveshare/e-Paper/issues/30