Prevent sending empty Content-Type header

server/handlers.go

@@ -970,7 +970,9 @@ func (s *Server) headHandler(w http.ResponseWriter, r *http.Request) {
 
 	remainingDownloads, remainingDays := metadata.remainingLimitHeaderValues()
 
-	w.Header().Set("Content-Type", contentType)
+	if contentType != "" {
+		w.Header().Set("Content-Type", contentType)
+	}
 	if !useZstd {
 		w.Header().Set("Content-Length", strconv.FormatUint(contentLength, 10))
 	}
@@ -1039,7 +1041,9 @@ func (s *Server) getHandler(w http.ResponseWriter, r *http.Request) {
 
 	remainingDownloads, remainingDays := metadata.remainingLimitHeaderValues()
 
-	w.Header().Set("Content-Type", contentType)
+	if contentType != "" {
+		w.Header().Set("Content-Type", contentType)
+	}
 	if !useZstd {
 		w.Header().Set("Content-Length", strconv.FormatUint(contentLength, 10))
 	} else {