[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/Process.cpp

@@ -13,6 +13,10 @@ namespace wpi::uv {
 
 std::shared_ptr<Process> Process::SpawnArray(Loop& loop, std::string_view file,
                                              std::span<const Option> options) {
+  if (loop.IsClosing()) {
+    return nullptr;
+  }
+
   // convert Option array to libuv structure
   uv_process_options_t coptions;