filer: respect Content-Type on PUT

This is needed for the S3 gateway to conform to the S3 protocol -- the
server should always respect the Content-Type set by client.

weed/server/filer_server_handlers_write_autochunk.go

@@ -111,7 +111,10 @@ func (fs *FilerServer) doPostAutoChunk(ctx context.Context, w http.ResponseWrite
 func (fs *FilerServer) doPutAutoChunk(ctx context.Context, w http.ResponseWriter, r *http.Request, chunkSize int32, so *operation.StorageOption) (filerResult *FilerPostResult, md5bytes []byte, replyerr error) {
 
 	fileName := ""
-	contentType := ""
+	contentType := r.Header.Get("Content-Type")
+	if contentType == "application/octet-stream" {
+		contentType = ""
+	}
 
 	fileChunks, md5Hash, chunkOffset, err, smallContent := fs.uploadReaderToChunks(w, r, r.Body, chunkSize, fileName, contentType, so)
 	if err != nil {