check for too big overlay is done on the client side

frontend-js/src/main/js/gui/leftPanel/OverlayPanel.js

@@ -450,6 +450,8 @@ OverlayPanel.prototype.openAddOverlayDialog = function () {
       }
       if (fileContent === null) {
         GuiConnector.alert("Neither file was selected nor data was entered");
+      } else if (fileContent.length > 1024 * 256) {
+        GuiConnector.alert("File to big.<br>Please reduce file size or contact administrators.");
       } else {
         var data = {
           name: nameInput.value,