plot: Correct a couple SVG output errors

Plotting to closed lines for polygons in SVG.  Also correct the filled
polygon line width for non-copper zones.

Fixes: lp:1813964
* https://bugs.launchpad.net/kicad/+bug/1813964

pcbnew/plot_brditems_plotter.cpp

@@ -681,7 +681,7 @@ void BRDITEMS_PLOTTER::PlotFilledAreas( ZONE_CONTAINER* aZone )
             {
                 // Plot the filled area polygon.
                 // The area can be filled by segments or uses solid polygons
-                if( aZone->GetFillMode() == 0 ) // We are using solid polygons
+                if( aZone->GetFillMode() == ZONE_FILL_MODE::ZFM_POLYGONS ) // We are using solid polygons
                 {
                     m_plotter->PlotPoly( cornerList, FILLED_SHAPE, aZone->GetMinThickness(), &gbr_metadata );
                 }