Fix an infinite loop in flush

Closes rust-lang#57

src/gz.rs

@@ -664,4 +664,11 @@ mod tests {
             v == v2
         }
     }
+
+    #[test]
+    fn flush_after_write() {
+		let mut f = EncoderWriter::new(Vec::new(), Default);
+		write!(f, "Hello world").unwrap();
+		f.flush().unwrap();
+    }
 }

src/zio.rs

@@ -158,16 +158,17 @@ impl<W: Write, D: Ops> Write for Writer<W, D> {
     }
 
     fn flush(&mut self) -> io::Result<()> {
+        self.data.run_vec(&[], &mut self.buf, Flush::Sync).unwrap();
+
         // Unfortunately miniz doesn't actually tell us when we're done with
         // pulling out all the data from the internal stream. To remedy this we
         // have to continually ask the stream for more memory until it doesn't
         // give us a chunk of memory the same size as our own internal buffer,
         // at which point we assume it's reached the end.
         loop {
             try!(self.dump());
-
             let before = self.data.total_out();
-            self.data.run_vec(&[], &mut self.buf, Flush::Sync).unwrap();
+            self.data.run_vec(&[], &mut self.buf, Flush::None).unwrap();
             if before == self.data.total_out() {
                 break
             }