http: force socket encoding to be null

Otherwise the string triggers an assertion error in node_http_parser.c,
line 370:

    assert(Buffer::HasInstance(args[0]) == true);

because the first argument is not a Buffer object.
crypto: try moving read head in Peek()

Otherwise it might get stall (`Peek()` will return zero-length chunk)
in following situation:

1. `Write(kBufferLength)`
2. `Read(kBufferLength)`
3. `Write(anything)`
4. `Peek()` => `len=0`