Fix polygon shape move

Move vector should not affect start/end points as they are assumed to
always be 0,0. Polygon is defined by outline only.

(cherry-picked from 32674ef360)

pcbnew/class_drawsegment.cpp

@@ -79,8 +79,13 @@ const wxPoint DRAWSEGMENT::GetPosition() const
 
 void DRAWSEGMENT::Move( const wxPoint& aMoveVector )
 {
+    // Move vector should not affect start/end for polygon since it will
+    // be applied directly to polygon outline.
+    if( m_Shape != S_POLYGON )
+    {
         m_Start += aMoveVector;
         m_End += aMoveVector;
+    }
 
     switch ( m_Shape )
     {