Plot pad outlines on Fab files: fix many issues. Depending on

plotter type and pad type, the plotted shapes were not always the outlines,
but a outline inside the pad shape (due to legacy reasons). In many cases the
plotted shape was in fact incorrect. Now the actual pads outlines are plotted
without modification.
From Master branch

common/plotters/HPGL_plotter.cpp

@@ -2,7 +2,7 @@
  * This program source code file is part of KiCad, a free EDA CAD application.
  *
  * Copyright (C) 2017 Jean-Pierre Charras, jp.charras at wanadoo.fr
- * Copyright (C) 2020-2021 KiCad Developers, see AUTHORS.txt for contributors.
+ * Copyright (C) 2020-2022 KiCad Developers, see AUTHORS.txt for contributors.
  *
  * This program is free software; you can redistribute it and/or
  * modify it under the terms of the GNU General Public License
@@ -486,7 +486,7 @@ void HPGL_PLOTTER::PlotPoly( const std::vector<wxPoint>& aCornerList, FILL_T aFi
         m_current_item->content << hpgl_end_polygon_cmd; // Close, fill polygon and draw outlines
         m_current_item->pen_returns = true;
     }
-    else if( aWidth > 0 )
+    else if( aWidth != 0 )
     {
         // Plot only the polygon outline.
         for( unsigned ii = 1; ii < aCornerList.size(); ii++ )
@@ -659,10 +659,10 @@ void HPGL_PLOTTER::FlashPadCircle( const wxPoint& pos, int diametre,
         // if filled mode, the pen diameter is removed from diameter
         // to keep the pad size
         radius -= KiROUND( penDiameter ) / 2;
-    }
 
-    if( radius < 0 )
-        radius = 0;
+        if( radius < 0 )
+            radius = 0;
+    }
 
     double rsize = userToDeviceSize( radius );