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
(cherry picked from commit 93abb208)
Reviewed-on: https://gerrit.libreoffice.org/3793Reviewed-by: Miklos Vajna <vmiklos@suse.cz>
Tested-by: Miklos Vajna <vmiklos@suse.cz>

oox/source/export/drawingml.cxx

@@ -1500,8 +1500,7 @@ void DrawingML::WriteFill( Reference< XPropertySet > xPropSet )
     FillStyle aFillStyle( FillStyle_NONE );
     xPropSet->getPropertyValue( S( "FillStyle" ) ) >>= aFillStyle;
 
-    if( aFillStyle == FillStyle_NONE ||
-        aFillStyle == FillStyle_HATCH )
+    if( aFillStyle == FillStyle_HATCH )
         return;
 
     switch( aFillStyle )
@@ -1515,6 +1514,9 @@ void DrawingML::WriteFill( Reference< XPropertySet > xPropSet )
     case ::com::sun::star::drawing::FillStyle_BITMAP :
         WriteBlipFill( xPropSet, S( "FillBitmapURL" ) );
         break;
+    case ::com::sun::star::drawing::FillStyle_NONE:
+        mpFS->singleElementNS( XML_a, XML_noFill, FSEND );
+        break;
     default:
         ;
     }