let us be explicit about default values

Different MSO versions behave differently in respect to the default
values. 2007 is not compliant to OOXML and is what our export filter
expects, 2010+ are compliant to OOXML and therefore our charts look
awful.

Change-Id: If301d878a1603ed9835884cfbb9ed9c902526ba0

oox/source/export/drawingml.cxx

@@ -1522,8 +1522,7 @@ void DrawingML::WriteFill( Reference< XPropertySet > xPropSet )
     FillStyle aFillStyle( FillStyle_NONE );
     xPropSet->getPropertyValue( "FillStyle" ) >>= aFillStyle;
 
-    if( aFillStyle == FillStyle_NONE ||
-        aFillStyle == FillStyle_HATCH )
+    if( aFillStyle == FillStyle_HATCH )
         return;
 
     switch( aFillStyle )
@@ -1537,6 +1536,9 @@ void DrawingML::WriteFill( Reference< XPropertySet > xPropSet )
     case ::com::sun::star::drawing::FillStyle_BITMAP :
         WriteBlipFill( xPropSet, "FillBitmapURL" );
         break;
+    case ::com::sun::star::drawing::FillStyle_NONE:
+        mpFS->singleElementNS( XML_a, XML_noFill, FSEND );
+        break;
     default:
         ;
     }