coverity#703935 Unchecked return value

Change-Id: I31ce141955a3beadb60368fc8238bfe0507b1566
Reviewed-on: https://gerrit.libreoffice.org/57782
Tested-by: Jenkins
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

cui/source/dialogs/cuigrfflt.cxx

@@ -248,7 +248,7 @@ Graphic GraphicFilterMosaic::GetFilteredGraphic( const Graphic& rGraphic,
         if (BitmapFilter::Filter(aAnim, BitmapMosaicFilter(aSize.getWidth(), aSize.getHeight())))
         {
             if( IsEnhanceEdges() )
-                BitmapFilter::Filter(aAnim, BitmapSharpenFilter());
+                (void)BitmapFilter::Filter(aAnim, BitmapSharpenFilter());
 
             aRet = aAnim;
         }