Kernel: Verify Process coredump threads are empty

Author: https://github.com/gmta
Commit: ab840423a8
Pull-request: https://github.com/SerenityOS/serenity/pull/8052
Issue: https://github.com/SerenityOS/serenity/issues/7289

Kernel/Process.cpp

@@ -565,6 +565,7 @@ void Process::die()
     // slave owner, we have to allow the PTY pair to be torn down.
     m_tty = nullptr;
 
+    VERIFY(m_threads_for_coredump.is_empty());
     for_each_thread([&](auto& thread) {
         m_threads_for_coredump.append(thread);
     });