fix maybe uninit warning

triggered when compiling target Bounding_volumes

Bounding_volumes/include/CGAL/Min_ellipse_2.h

@@ -360,7 +360,20 @@ class Min_ellipse_2 {
     
     // default constructor
     inline
-    Min_ellipse_2( const Traits& traits = Traits())
+    Min_ellipse_2()
+        : n_support_points( 0)
+    {
+        // allocate support points' array
+        support_points = new Point[ 5];
+    
+        // initialize ellipse
+        tco.ellipse.set();
+    
+        CGAL_optimisation_postcondition( is_empty());
+    }
+
+    inline
+    Min_ellipse_2( const Traits& traits )
         : tco( traits), n_support_points( 0)
     {
         // allocate support points' array