title: FineUploader UI shows thumbnail on file select, but not drag-n-drop
body: <p>Using React and FineUploader 5.14.2-rc1 in UI mode. Uploads work great, but the displayed thumbnails are inconsistent. When I click the component and select a file from the system file selection dialog, the file is represented by a thumbnail of the image. But when I drag the same file and drop it on the component, it displays a generic file icon rather than an image thumbnail. I'm assuming this is a configuration problem, but I can't find anything germane in the documentation. Here's the relevant component: </p>
  
  <pre><code>import FineUploaderS3 from 'fine-uploader-wrappers/s3'
  import Gallery from 'react-fine-uploader'
  
  export default class FileUploader extends React.Component {
  
      constructor(props){
          super(props)
  
          this.state = {
              showModal: props.showModal || false,
              fileName: props.fileName,
              s3Key: props.s3Key,
              title: props.title,
              description: props.description,
              fileUrl: props.fileUrl,
              success: props.success || true,
          }
  
          let uploaderInstance = null
  
          this.uploader = () =&gt;{
              uploaderInstance = new FineUploaderS3({
                  options: {
                      chunking: {
                          enabled: true 
                      },
                      resume: {
                          enabled: true 
                      },
                      request: {
                          endpoint: 'http://ourbucketurl',
                          accessKey: ourAccessKeyId,
                      },
                      signature: {
                          endpoint: '/api/s3handler', 
                      },
                      uploadSuccess: {
                          endpoint: '/api/s3uploadsuccess', 
                      },
                      callbacks: {
                          onComplete: this.uploadCompleteHandler
                      },
                  }
              })
  
              return uploaderInstance
          }
  
          this.uploadCompleteHandler = (id, name, responseJSON) =&gt; {
              this.setState({showModal: responseJSON.success,
                  s3Key: responseJSON.key,
                  fileName: responseJSON.name,
                  fileUrl: `https://ourbucketurl/${responseJSON.key}`})
          }
  
      render() {
  
          return &lt;div&gt;
              &lt;Gallery uploader={this.uploader()} /&gt;
          &lt;/div&gt;
      }
  }
  </code></pre>
  
  <p>I can put this component anywhere, and files upload without incident.</p>
  
  <p>The problem occurs regardless of browser. What do I need to do to show thumbnails consistently regardless of how the user invokes the upload operation?</p>