[wpinet] uv: Stop creating handles when closing loop (#5102)

This prevents EventLoopRunner::Stop() from hanging in the case when
new handles are created after the async walk closes all the handles.

wpinet/src/main/native/cpp/uv/Check.cpp

@@ -9,6 +9,9 @@
 namespace wpi::uv {
 
 std::shared_ptr<Check> Check::Create(Loop& loop) {
+  if (loop.IsClosing()) {
+    return nullptr;
+  }
   auto h = std::make_shared<Check>(private_init{});
   int err = uv_check_init(loop.GetRaw(), h->GetRaw());
   if (err < 0) {
@@ -20,6 +23,9 @@ std::shared_ptr<Check> Check::Create(Loop& loop) {
 }
 
 void Check::Start() {
+  if (IsLoopClosing()) {
+    return;
+  }
   Invoke(&uv_check_start, GetRaw(), [](uv_check_t* handle) {
     Check& h = *static_cast<Check*>(handle->data);
     h.check();