PPTX export: fix size of shape for slide narrations

This was invisible in PowerPoint without explicit stretching.

Change-Id: I29b9f23eba6d59436cb1b6d15c9840794f932e69
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/109778
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins

oox/source/export/shapes.cxx

@@ -1238,6 +1238,14 @@ void ShapeExport::WriteGraphicObjectShapePart( const Reference< XShape >& xShape
     if ( pGraphic || bStretch )
         pFS->singleElementNS(XML_a, XML_stretch);
 
+    if (bHasMediaURL)
+    {
+        // Graphic of media shapes is always stretched.
+        pFS->startElementNS(XML_a, XML_stretch);
+        pFS->singleElementNS(XML_a, XML_fillRect);
+        pFS->endElementNS(XML_a, XML_stretch);
+    }
+
     pFS->endElementNS( mnXmlNamespace, XML_blipFill );
 
     // visual shape properties

sd/qa/unit/export-tests-ooxml1.cxx

@@ -1336,6 +1336,12 @@ void SdOOXMLExportTest1::testNarrationMimeType()
     // i.e. the bitmap of the narration was lost, some default placeholder was exported instead.
     CPPUNIT_ASSERT_EQUAL(static_cast<tools::Long>(256), aBitmapEx.GetSizePixel().Height());
 
+    // Without the accompanying fix in place, this test would have failed with:
+    // - Expected: 1
+    // - Actual  : 0
+    // i.e. p:blipFill was missing its a:stretch child element, so the shape was invisible.
+    assertXPath(pSlideDoc, "/p:sld/p:cSld/p:spTree/p:pic/p:blipFill/a:stretch/a:fillRect", 1);
+
     xDocShRef->DoClose();
 }