Fixed
- ACARS and VDL2 could silently stop decoding on macOS. On a Mac the decoder's output is read through a pseudo-terminal that rejected anything that wasn't valid UTF-8, so a single corrupt byte from radio noise or a damaged frame stopped the reader while acarsdec/dumpvdl2 carried on running, and no more messages appeared. Invalid bytes are now replaced, as they already were on Linux. (#376)