pcbnew: Fix polygon comparison () for end

This is a v5-only fix incorporating 2c5876e and 72da237 into the 5
branch to resolve a crash when parsing invalid polygons.

Fixes #3752 | https://gitlab.com/kicad/code/kicad/issues/3752

include/geometry/shape_poly_set.h

@@ -165,7 +165,16 @@ class SHAPE_POLY_SET : public SHAPE
 
             operator bool() const
             {
-                return m_currentPolygon <= m_lastPolygon;
+                if( m_currentPolygon < m_lastPolygon )
+                    return true;
+
+                if( m_currentPolygon != m_poly->OutlineCount() - 1 )
+                    return false;
+
+                const auto& currentPolygon = m_poly->CPolygon( m_currentPolygon );
+
+                return m_currentContour < (int) currentPolygon.size() - 1
+                           || m_currentVertex < currentPolygon[m_currentContour].PointCount();
             }
 
             /**