wxComboBox::SetString trashes associated data

[aasselin]

when calling mycombo->SetString(0, "hello") associated client data is lost, as well as type of client data if there is a single item in the combo

the implementation is using Delete(n); Insert(s,n); maybe it should be GetComboPeer()->RemoveItem(n); GetComboPeer()->InsertItem(n,s) ?

[vadz]

This looks correct to me. I've also looked at ​NSComboBox to see if there was a way to replace the item directly, without removing and inserting it, but there doesn't seem to be any way to do it, so this patch is the best we can do.

Of course, as mentioned in #12419, we really ought to be using a data source with the combobox instead of mucking with its items anyhow, to be able to implement sorting in it. But this will have to wait :-(

[VZ]

(In [71942]) Preserve client data in wxComboBox::SetString() in wxOSX/Cocoa.

Don't reset the client data to NULL when we're just changing the item text.

Closes #14146.