Make mainloopData explicit for increase/decrease of data availability, and then store it in the DVS128 module
for usage by the acquisition thread.
Fix freeing on init-error in DVS128 module.
Check that the packet we get has actual content. NULL packets are possible!!!
Ensure that once a second the mainloop is run anyway, even if no data is available.
This is so that producers may be re-started after a shutdown or devices plugged in later on.