Don't wait for display frame if interrupt pending

[dhalbert]

common_hal_displayio_display_wait_for_frame() would call the background tasks over and over. If a reload was pending, displayio_refresh_displays() would stop refreshing, but common_hal_displayio_display_wait_for_frame() didn't know that.

The effect was that writes to CIRCUITPY would cause the board to apparently freeze (because the display was frozen). It was really cycling in the background task, never to return.

Details:

• Check for pending interrupts in common_hal_displayio_display_wait_for_frame().
• In displayio_refresh_displays():
  • Check for KeyboardInterrupt immediately (otherwise sometimes two ctrl-C's were needed)
  • Don't bother to re- raise ReloadException if it was already raised.

I believe this fixes freezes seen by @ladyada, who will test in a few days.

This may or may not have something to do with #1577.

[dhalbert]

@jerryneedell you tested this, I think? Could you approve so we can get wider testing on this? Thanks.

[jerryneedell]

I complied and tested this on pyportal and feather_m4. I did not have any issues with it. It did not resolve the SPI issues I have been seeing.

[tannewt]

Looks good to me too! Thanks for fixing this while I was away.