bufread::generic::Decoder: don't reinitialize on reader EOF

If `multiple_members` is enabled, the `bufread::generic::Decoder` will
attempt to reinitialise the decoder inside `State::Flushing`, even if
the reason it entered that state was due to the reader returning an EOF.
This will result in an attempt to read past EOF, which is highly
undesirable to say the least.

To fix this, force `multiple_members` to `false` when we get an EOF
condition from the reader.

Author: eeeeeta

src/futures/bufread/generic/decoder.rs

@@ -70,6 +70,9 @@ impl<R: AsyncBufRead, D: Decode> Decoder<R, D> {
                 State::Decoding => {
                     let input = ready!(this.reader.as_mut().poll_fill_buf(cx))?;
                     if input.is_empty() {
+                        // Avoid attempting to reinitialise the decoder if the reader
+                        // has returned EOF.
+                        *this.multiple_members = false;
                         State::Flushing
                     } else {
                         let mut input = PartialBuffer::new(input);