geometry: constructor for SHAPE_RECT from a BOX2

libs/kimath/include/geometry/shape_rect.h

@@ -46,6 +46,16 @@ public:
         m_h( 0 )
     {}
 
+    /**
+     * Create a rectangle defined by a BOX2.
+     */
+    SHAPE_RECT( const BOX2I& aBox ) :
+        SHAPE( SH_RECT ),
+        m_p0( aBox.GetPosition() ),
+        m_w( aBox.GetWidth() ),
+        m_h( aBox.GetHeight() )
+    {}
+
     /**
      * Create a rectangle defined by top-left corner (aX0, aY0), width aW and height aH.
      */