message: fix error when text is null/undef
diff: @@ -1130,7 +1130,7 @@ export function genXmlTextBody(slideObj: ISlideObject | ITableCell): string {
  }
  // C: If text string has line-breaks, then create a separate text-object for each (much easier than dealing with split inside a loop below)
  - if (obj.options.breakLine || obj.text.indexOf(CRLF) > -1) {
  + if (obj.options.breakLine || (obj.text || '').indexOf(CRLF) > -1) {
  obj.text.split(CRLF).forEach((line, lineIdx) => {
  // Add line-breaks if not bullets/aligned (we add CRLF for those below in STEP 3)
  // NOTE: Use "idx>0" so lines wont start with linebreak (eg:empty first line)
  