message: self-close <a:pPr> tag when no child
diff: @@ -905,9 +905,14 @@ function genXmlParagraphProperties(textObj: ISlideObject | TextProps, isDefault:
  // B: Close Paragraph-Properties
  // IMPORTANT: strXmlLnSpc, strXmlParaSpc, and strXmlBullet require strict ordering - anything out of order is ignored. (PPT-Online, PPT for Mac)
  - paragraphPropXml += '>' + strXmlLnSpc + strXmlParaSpc + strXmlBullet
  - if (isDefault) paragraphPropXml += genXmlTextRunProperties(textObj.options, true)
  - paragraphPropXml += '</' + tag + '>'
  + let childPropXml = strXmlLnSpc + strXmlParaSpc + strXmlBullet;
  + if (isDefault) childPropXml += genXmlTextRunProperties(textObj.options, true)
  + if (childPropXml) {
  + paragraphPropXml += '>' + childPropXml + '</' + tag + '>'
  + } else {
  + // self-close when no child props
  + paragraphPropXml += '/>'
  + }
  }
  return paragraphPropXml
  