Application subclasss needs to handle parent delete_event

[alatiera]

Unrelated. The problem is that delete_event is NULL here and we currently don't handle that in the subclass bindings. We would have to check for which virtual methods it is valid to have NULL there and then what the default behaviour should be (another thing for which we don't have g-i annotations...). That requires diving into the C code. I've done that for the things in gio and gstreamer, but nowhere else.

In this specific case, instead of panicking at that line it should return false here if it's NULL.

Originally posted by @sdroege in gtk-rs/examples#256 (comment)

[sdroege]

The title is wrong. It's not about handling it instead of setting to NULL, but we need to handle the parent one being NULL by implementing default behaviour.

In specific, the expect() here should be replaced by an unwrap_or(false):

gtk/src/subclass/widget.rs

Line 453 in e55bd4d

.expect("No parent class impl for \"delete_event\"");

[sdroege]

Also CC @BrainBlasted