Fix wxPGChoices::Set method.

There is no need to check if referenced array with values is valid since "reference cannot be bound to dereferenced null pointer in well-defined C++ code". Moreover, conditional call of wxPGChoices::Add() methods (one with explicit parameter and one with default one) is not necessary.

This is the backport of r78343.
See #16759 (http://trac.wxwidgets.org/ticket/16759).

include/wx/propgrid/property.h

@@ -1050,10 +1050,7 @@ public:
               const wxArrayInt& values = wxArrayInt() )
     {
         Free();
-        if ( &values )
         Add(labels,values);
-        else
-            Add(labels);
     }
 
     // Creates exclusive copy of current choices