Don't busy loop if we get an end of stream during handshake
Don't busy loop if we get an end of stream during handshake

`try_read_buf` returns `Ok(0)` on EoS but that case wasn't handled in
the `read_handshake` code. This means that a connection closing during
the handshake was leaving the socket behind in readable state and we
were busy looping trying to read from it.

Fixes #195

housleyjk/ws-rs