tdf#89329: use unique_ptr for pImpl in dialog

Change-Id: Ic08e35a08f3f72383be305e3458b83fe06e3e1a5
Reviewed-on: https://gerrit.libreoffice.org/25902Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>

include/vcl/dialog.hxx

@@ -37,7 +37,7 @@ public:
 
 private:
     VclPtr<Dialog>  mpPrevExecuteDlg;
-    DialogImpl*     mpDialogImpl;
+    std::unique_ptr<DialogImpl>     mpDialogImpl;
     long            mnMousePositioned;
     bool            mbInExecute;
     bool            mbInClose;

vcl/source/window/dialog.cxx

@@ -362,7 +362,7 @@ void Dialog::ImplInitDialogData()
     mpContentArea.clear();
     mpActionArea.clear();
     mnMousePositioned       = 0;
-    mpDialogImpl            = new DialogImpl;
+    mpDialogImpl.reset(new DialogImpl);
 }
 
 void Dialog::ImplInit( vcl::Window* pParent, WinBits nStyle, InitFlag eFlag )
@@ -583,8 +583,7 @@ Dialog::~Dialog()
 
 void Dialog::dispose()
 {
-    delete mpDialogImpl;
-    mpDialogImpl = nullptr;
+    mpDialogImpl.reset();
     mpPrevExecuteDlg.clear();
     mpActionArea.clear();
     mpContentArea.clear();