fix(http): fix encoding when buffer is full

src/http/h1/encode.rs

@@ -54,9 +54,12 @@ impl Encoder {
                 chunked.encode(w, msg)
             },
             Kind::Length(ref mut remaining) => {
+                if msg.is_empty() {
+                    return Ok(0);
+                }
                 let n = {
                     let max = cmp::min(*remaining as usize, msg.len());
-                    trace!("sized write, len = {}", max);
+                    trace!("sized write, len = {}, remaining = {}", max, remaining);
                     let slice = &msg[..max];
 
                     try!(w.write_atomic(&[slice]))