Honor Accept-Encoding if it was set in the request, close AsyncHttpClient#686

Author: Stephane Landelle

providers/netty/src/main/java/org/asynchttpclient/providers/netty/request/NettyRequestFactory.java

@@ -277,8 +277,11 @@ public NettyRequest newNettyRequest(Request request, UriComponents uri, boolean
             if (isNonEmpty(request.getCookies()))
                 headers.set(HttpHeaders.Names.COOKIE, CookieEncoder.encode(request.getCookies()));
 
-            if (config.isCompressionEnabled())
-                headers.set(HttpHeaders.Names.ACCEPT_ENCODING, GZIP_DEFLATE);
+            if (config.isCompressionEnabled()) {
+                if (!headers.contains(HttpHeaders.Names.ACCEPT_ENCODING))
+                    headers.set(HttpHeaders.Names.ACCEPT_ENCODING, GZIP_DEFLATE);
+            } else
+                headers.remove(HttpHeaders.Names.ACCEPT_ENCODING);
         }
 
         if (body != null) {