I found this issue experimenting with the `ftrivial-auto-var-init=pattern` compile flag. `keystoreEventHandlers()` returns a `WT_EVENT_HANDLER*` but leaves the `handle_general` member uninitialized. This `WT_EVENT_HANDLER*` eventually gets passed to `wiredtiger_open`, which has a check like `if (event_handler != NULL && event_handler>handle_general != NULL)` before calling `handle_general`. If `handle_general` doesn't happen to get zero-initialized, this can crash. This change explicitly initializes it to `nullptr` to avoid that.