Use malloc for ESP32 data buffers to avoid issues

More details here: https://github.com/pixelmatix/AnimatedGIFs/issues/26

https://github.com/pixelmatix/SmartMatrix/issues/69

I think this shows how to allocate the block needed for AnimatedGIF with malloc (after allocating mymemorypool with malloc):

https://github.com/bitbank2/AnimatedGIF/issues/8#issuecomment-676480432
