Re-add wxFD_OVERWRITE_PROMPT and wxFD_FILE_MUST_EXIST to wxGenericFileDialog.

Support for these styles was accidentally removed in r48733, re-add them back.

Closes #16652.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78080 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/filedlgg.cpp

@@ -336,9 +336,35 @@ void wxGenericFileDialog::OnOk( wxCommandEvent &WXUNUSED(event) )
     if (selectedFiles.Count() == 0)
         return;
 
+    const wxString& path = selectedFiles[0];
+
     if (selectedFiles.Count() == 1)
     {
-        SetPath( selectedFiles[0] );
+        SetPath(path);
+    }
+
+    // check that the file [doesn't] exist if necessary
+    if ( HasFdFlag(wxFD_SAVE) && HasFdFlag(wxFD_OVERWRITE_PROMPT) &&
+                wxFileExists(path) )
+    {
+        if ( wxMessageBox
+             (
+                wxString::Format
+                (
+                    _("File '%s' already exists, do you really want to overwrite it?"),
+                    path
+                ),
+                _("Confirm"),
+                wxYES_NO
+             ) != wxYES)
+            return;
+    }
+    else if ( HasFdFlag(wxFD_OPEN) && HasFdFlag(wxFD_FILE_MUST_EXIST) &&
+                    !wxFileExists(path) )
+    {
+        wxMessageBox(_("Please choose an existing file."), _("Error"),
+                     wxOK | wxICON_ERROR );
+        return;
     }
 
     EndModal(wxID_OK);