add content-length header

Author: YazeedAlKhalaf

pmtiles/server.go

@@ -526,6 +526,8 @@ func (server *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) int {
 		w.Header().Set(k, v)
 	}
 	if statusCode == 200 {
+		w.Header().Set("Content-Length", strconv.Itoa(len(body)))
+
 		lrw := &loggingResponseWriter{w, 200}
 		// handle if-match, if-none-match request headers based on response etag
 		http.ServeContent(