fix crash on image with no data

src/widgets/image-preview.jsx

@@ -55,7 +55,7 @@ export default class ImagePreview extends React.PureComponent {
       <div id="image-preview">
         <div id="image-preview-caption-panel">
           {!this.props.onSendMessage ?
-            <a href={this.props.content.url} download={this.props.content.name}>
+            <a href={this.props.content.url} download={true}>
               <i className="material-icons">file_download</i> <FormattedMessage
                 id="download_action" defaultMessage="download" description="Call to action [download]" />
             </a>

src/widgets/lazy-image.jsx

@@ -31,6 +31,7 @@ export default class LazyImage extends React.PureComponent {
     if (prevProps.whenDone != this.props.whenDone) {
       this.setState({src: 'img/placeholder.png', style: {...this.state.style, padding: '4px'}});
       this.props.whenDone
+        .promise
         .then(data => this.setState({src: data.src, style: {...this.state.style, padding: 0}}))
         .catch(() => this.setState({src: 'img/broken_image.png'}));
     }