Correctly initialize wxGtkPrintNativeData members.

In particular, create a valid GtkPrintOperation object instead of using an
uninitialized pointer to it in wxGtkPrintDialog::ShowModal(), resulting in
crashes or, at best, GTK errors.

Closes #12483.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65828 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/print.h

@@ -196,7 +196,6 @@ public:
     GtkPrintSettings* GetPrintConfig() { return m_config; }
     void SetPrintConfig( GtkPrintSettings * config );
 
-    void SetPrintJob( GtkPrintOperation *job ) { m_job = job; }
     GtkPrintOperation* GetPrintJob() { return m_job; }
 
     GtkPrintContext *GetPrintContext() { return m_context; }