message: Adjust MIME type of upload confirmation if needed
  This filters the MIME type of uploaded files to ensure we display safely.
diff: @@ -20,6 +20,7 @@ import * as sdk from '../../../index';
  import { _t } from '../../../languageHandler';
  import filesize from "filesize";
  import { replaceableComponent } from "../../../utils/replaceableComponent";
  +import { getBlobSafeMimeType } from '../../../utils/blobs';
  interface IProps {
  file: File;
  @@ -31,6 +32,7 @@ interface IProps {
  @replaceableComponent("views.dialogs.UploadConfirmDialog")
  export default class UploadConfirmDialog extends React.Component<IProps> {
  private objectUrl: string;
  + private mimeType: string;
  static defaultProps = {
  totalFiles: 1,
  @@ -39,7 +41,13 @@ export default class UploadConfirmDialog extends React.Component<IProps> {
  constructor(props) {
  super(props);
  - this.objectUrl = URL.createObjectURL(props.file);
  + // Create a fresh `Blob` for previewing (even though `File` already is
  + // one) so we can adjust the MIME type if needed.
  + this.mimeType = getBlobSafeMimeType(props.file.type);
  + const blob = new Blob([props.file], { type:
  + this.mimeType,
  + });
  + this.objectUrl = URL.createObjectURL(blob);
  }
  componentWillUnmount() {
  @@ -76,7 +84,7 @@ export default class UploadConfirmDialog extends React.Component<IProps> {
  }
  let preview;
  - if (this.props.file.type.startsWith('image/')) {
  + if (this.mimeType.startsWith('image/')) {
  preview = <div className="mx_UploadConfirmDialog_previewOuter">
  <div className="mx_UploadConfirmDialog_previewInner">
  <div><img className="mx_UploadConfirmDialog_imagePreview" src={this.objectUrl} /></div>
  