Error: if <system_new_file> is in brotli(.br) format

[ShanuDey]

<system_new_file> should be in .dat format. If the new file in brotli(.br) format then there should be an error to break the process.
Signed-off-by: ShanuDey sd4shanudey@gmail.com

[mirh]

Mhh, and maybe if it isn't .br.. a warning could be emitted if the file doesn't have a .dat extension?
(too bad this also doesn't have any kind of header or magic number either)

[davwheat]

If anyone needs to know how to convert the .new.dat.br to .new.dat...

1. sudo apt install brotli
2. brotli --decompress xxx.new.dat.br
3. Done!