pcbnew: Treat circular ovals as circles

The oval clearance adds an edge on the 0-length side of a circular oval.
This is not needed and can affect the fill algorithm.  Instead, we treat
round ovals as circles for pad polygons

Fixes: lp:1849846
* https://bugs.launchpad.net/kicad/+bug/1849846

pcbnew/board_items_to_polygon_shape_transform.cpp

@@ -723,6 +723,14 @@ void D_PAD::TransformShapeWithClearanceToPolygon( SHAPE_POLY_SET& aCornerBuffer,
 
     case PAD_SHAPE_OVAL:
         // An oval pad has the same shape as a segment with rounded ends
+        // If the oval is actually a circle (same x/y size), treat it the same
+        if( dx == dy )
+        {
+            dx = KiROUND( dx * aCorrectionFactor );
+            TransformCircleToPolygon( aCornerBuffer, padShapePos, dx,
+                                      aCircleToSegmentsCount );
+        }
+        else
         {
             int width;
             wxPoint shape_offset;