invalid handle race condition in ring buffer and perf buffer

Summary

ebpf_ring_buffer_set_wait_handle silently fails when passed ebpf_handle_invalid.

Problem

Invalid handle failure on cleanup

Both ring_buffer__free and perf_buffer__free call ebpf_map_set_wait_handle(..., ebpf_handle_invalid) to clear the wait event during teardown. The current code
passes (HANDLE)-1 directly to ObReferenceObjectByHandle, which fails in kernel mode, causing the cleanup to silently fail. The old event reference is leaked and the
stale pointer is never cleared from kernel_page->wait_event.

Note: This bug is masked in user-mode tests because the usersim ObReferenceObjectByHandle mock accepts any handle value including (HANDLE)-1.

Impact

- Affects both BPF_MAP_TYPE_RINGBUF and BPF_MAP_TYPE_PERF_EVENT_ARRAY (shared code path)