[bug] v.next is not proper cleared for re-enqueue a completion between different queues

[dacheng-gao]

https://github.com/mitchellh/libxev/blob/main/src/queue.zig#L24C13-L24C36

/// Enqueue a new element to the back of the queue.
pub fn push(self: *Self, v: *T) void {
    assert(v.next == null);

    if (self.tail) |tail| {
        // If we have elements in the queue, then we add a new tail.
        tail.next = v;
        self.tail = v;
    } else {
        // No elements in the queue we setup the initial state.
        self.head = v;
        self.tail = v;
    }
}

I got error due to the assert while run benchmark for my project, here is the backtrace:

(lldb) bt
* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGABRT
    frame #0: 0x0000000198051388 libsystem_kernel.dylib`__pthread_kill + 8
    frame #1: 0x000000019808a88c libsystem_pthread.dylib`pthread_kill + 296
    frame #2: 0x0000000197f93c60 libsystem_c.dylib`abort + 124
    frame #3: 0x0000000100009dbc tinyproxy_zig`posix.abort at posix.zig:710:29
    frame #4: 0x0000000100005afc tinyproxy_zig`debug.defaultPanic(msg=(ptr = "reached unreachable code", len = 24), first_trace_addr=(data = 4294999376, some = '\x01')) at debug.zig:676:16
    frame #5: 0x000000010000d5b8 tinyproxy_zig`debug.FullPanic((function 'defaultPanic')).reachedUnreachable at debug.zig:63:17
    frame #6: 0x0000000100007d50 tinyproxy_zig`debug.assert(ok=false) at debug.zig:522:14
  * frame #7: 0x00000001000a388c tinyproxy_zig`queue.Intrusive(self=0x00000001002c0028, v=0x000000010480f720).push at queue.zig:24:19
    frame #8: 0x00000001000a1414 tinyproxy_zig`backend.kqueue.Loop.submit(self=0x00000001002c0000) at kqueue.zig:249:38
    frame #9: 0x00000001000a5570 tinyproxy_zig`backend.kqueue.Loop.tick(self=0x00000001002c0000, wait=1) at kqueue.zig:357:24
    frame #10: 0x00000001000a6ecc tinyproxy_zig`backend.kqueue.Loop.run(self=0x00000001002c0000, mode=once) at kqueue.zig:287:35
    frame #11: 0x00000001000a7110 tinyproxy_zig`asyncio.Executor.tick(self=0x0000000100200000) at asyncio.zig:61:26
    frame #12: 0x00000001000a737c tinyproxy_zig`asyncio.runCoro__anon_20532(exec=0x0000000100200000, frame=<unavailable>) at asyncio.zig:93:45
    frame #13: 0x00000001000ad16c tinyproxy_zig`asyncio.run__anon_20251(exec=0x0000000100200000) at asyncio.zig:83:16
    frame #14: 0x00000001000ad4d4 tinyproxy_zig`main.main at main.zig:35:16
    frame #15: 0x00000001000ad988 tinyproxy_zig`start.main [inlined] start.callMain at start.zig:656:37
    frame #16: 0x00000001000ad97c tinyproxy_zig`start.main [inlined] start.callMainWithArgs at start.zig:616:20
    frame #17: 0x00000001000ad904 tinyproxy_zig`start.main(c_argc=1, c_argv=0x000000016fdff610, c_envp=0x000000016fdff620) at start.zig:631:28
    frame #18: 0x0000000197ceab98 dyld`start + 6076
(lldb) frame var
(queue.Intrusive(backend.kqueue.Completion) *) self = 0x00000001002c0028
(backend.kqueue.Completion *) v = 0x000000010480f720
(lldb) print v.next
(backend.kqueue.Completion *) 0x000000010481f720

apparently, v.next is not null.