Handle empty bytes multipart, close AsyncHttpClient#1089

Author: slandelle

src/main/java/com/ning/http/client/multipart/MultipartBody.java

@@ -225,6 +225,12 @@ private int writeCurrentFile(ByteBuffer buffer) throws IOException {
 
     private int writeCurrentBytes(ByteBuffer buffer, int length) throws IOException {
 
+        if (currentBytes.length == 0) {
+            currentBytesPosition = -1;
+            currentBytes = null;
+            return 0;
+        }
+
         int available = currentBytes.length - currentBytesPosition;
 
         int writeLength = Math.min(available, length);