oox: disable gradient fill grab-bag for PPTX

This was added in commit 2fcf3a87
(ooxml: preserve gradient shape fill, 2014-01-31), and assumes that the
theme colors can be preserved, as the theme definition is grab-bagged as
well.

But the theme is grab-bagged only for DOCX, not for PPTX, so skip
gradient grab-bag for PPTX, otherwise the gradient would refer to
incorrect colors in the theme.

Change-Id: I98e1c67d4b10e68916f81dd7fc508eb4146d506b
Reviewed-on: https://gerrit.libreoffice.org/67386Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins
(cherry picked from commit cfc1f4ea)
Reviewed-on: https://gerrit.libreoffice.org/67396Reviewed-by: Jan Holesovsky <kendy@collabora.com>
Tested-by: Jan Holesovsky <kendy@collabora.com>

oox/source/export/drawingml.cxx

@@ -407,7 +407,9 @@ void DrawingML::WriteGradientFill( const Reference< XPropertySet >& rXPropSet )
         }
 
         // check if an ooxml gradient had been imported and if the user has modified it
-        if( EqualGradients( aOriginalGradient, aGradient ) )
+        // Gradient grab-bag depends on theme grab-bag, which is implemented
+        // only for DOCX.
+        if( EqualGradients( aOriginalGradient, aGradient ) && GetDocumentType() == DOCUMENT_DOCX)
         {
             // If we have no gradient stops that means original gradient were defined by a theme.
             if( aGradientStops.hasElements() )

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

@@ -885,6 +885,12 @@ void SdOOXMLExportTest1::testTdf94238()
     CPPUNIT_ASSERT_EQUAL(static_cast<sal_Int16>(100), aGradient.YOffset);
     CPPUNIT_ASSERT_EQUAL(static_cast<sal_Int16>(39), aGradient.Border);
 
+    // Without the accompanying fix in place, this test would have failed with
+    // 'Expected: 0, Actual  : 10592673', i.e. the start color of the gradient
+    // was incorrect.
+    CPPUNIT_ASSERT_EQUAL(static_cast<sal_Int32>(0), aGradient.StartColor);
+    CPPUNIT_ASSERT_EQUAL(static_cast<sal_Int32>(0x8B8B8B), aGradient.EndColor);
+
     xDocShRef->DoClose();
 }