Call Add(), not Set(), from wxPGChoices ctors

There is no need to call Free() on a newly constructed object and Set()
is just Free() followed by Add().

No real changes.

include/wx/propgrid/property.h

@@ -724,7 +724,7 @@ public:
     wxPGChoices( const wxChar* const* labels, const long* values = NULL )
     {
         Init();
-        Set(labels,values);
+        Add(labels,values);
     }
 
     // Constructor.
@@ -734,7 +734,7 @@ public:
                  const wxArrayInt& values = wxArrayInt() )
     {
         Init();
-        Set(labels,values);
+        Add(labels,values);
     }
 
     // Simple interface constructor.