message: fix mimetype for M->D files
diff: @@ -486,12 +486,16 @@ export class MatrixEventProcessor {
  }
  private GetFilenameForMediaEvent(content: IMatrixEventContent): string {
  + let ext = "";
  + try {
  + ext = "." + mime.extension(content.info.mimetype);
  + } catch (err) { } // pass, we don't have an extension
  if (content.body) {
  if (path.extname(content.body) !== "") {
  return content.body;
  }
  - return `${path.basename(content.body)}.${mime.extension(content.info.mimetype)}`;
  + return path.basename(content.body) + ext;
  }
  - return "matrix-media." + mime.extension(content.info.mimetype);
  + return "matrix-media" + ext;
  }
  }
  