fix body bytes encoding in curl.py (#2322)

Author: auvipy

kombu/asynchronous/http/curl.py

@@ -252,7 +252,11 @@ def _setup_request(self, curl, request, buffer, headers, _pycurl=pycurl):
             setopt(meth, True)
 
         if request.method in ('POST', 'PUT'):
-            body = request.body.encode('utf-8') if request.body else b''
+            if not request.body:
+                body = b''
+            else:
+                body = request.body if isinstance(request.body, bytes) else request.body.encode('utf-8')
+            
             reqbuffer = BytesIO(body)
             setopt(_pycurl.READFUNCTION, reqbuffer.read)
             if request.method == 'POST':