remove insert placeholder event handler after upload success

Author: sangcheol12

web_src/js/features/comp/EditorUpload.ts

@@ -101,10 +101,10 @@ async function handleUploadFiles(editor, dropzoneEl, files, e) {
 
     // Placeholders should be inserted on uploading the thumnail.
     // If not, the check upload process may fail
-    dropzoneEl.dropzone.on('thumbnail', () => {
-      editor.insertPlaceholder(placeholder);
-    });
+    const handleInsertPlaceholder = () => editor.insertPlaceholder(placeholder); 
+    dropzoneEl.dropzone.on('thumbnail', handleInsertPlaceholder);
     await uploadFile(dropzoneEl, file); // the "file" will get its "uuid" during the upload
+    dropzoneEl.dropzone.off('thumbnail', handleInsertPlaceholder); 
     editor.replacePlaceholder(placeholder, generateMarkdownLinkForAttachment(file, {width, dppx}));
   }
 }