[670974] Use the underlying BaseStream to read bytes instead of trying to peek a...

[670974] Use the underlying BaseStream to read bytes instead of trying to peek a character.

Peeking a character as it turns out is a really bad idea as it involves the encoder
to pull characters.   If the PeekChar happens to read a byte that is part of a
UTF8 string that needs more characters to process we would end up with the reported
crash.

Atsushi Enomoto tracked this down, and the fix is to use the binaryreader.BaseStream
to directly call into ReadByte and Read without ever probing with PeekChar ().   It
is not really possible to use BinaryReader.ReadByte since this one can throw on
end-of-buffer conditions instead of returning -1