Re: base64 encoding crashes

[napalu]

It's a bug in base64.nim where encodeInternal() does not account for the space 
needed for newLine when the string to be encoded expands to the line length or 
a multiple thereof. Reported as 
[https://github.com/nim-lang/Nim/pull/5458](https://github.com/nim-lang/Nim/pull/5458)
 along with a proposed fix.