PinePhone: Megapixels segfault if camera hardware switch disabled

Taken from https://todo.sr.ht/~martijnbraam/Megapixels/54

plata-gl reported:

if a camera hardware switch in the PinePhone is disabled, Megapixels segfaults because it cannot find the cameras from the device config. It should just ignore this part of the config instead (it's a perfectly valid use case to disable e.g. the front camera and use only the back camera).