Kernel: Process now locks the mutex while modifying open files

This allows processes to be actually removed from the list instead
of dead locking

kernel/kernel/Process.cpp

@@ -52,10 +52,12 @@ namespace Kernel
 	}
 
 	void Process::exit()
+	{
 		{
 			LockGuard _(m_lock);
 			for (auto* thread : m_threads)
 				thread->terminate();
+		}
 		while (!m_threads.empty())
 			PIT::sleep(1);
 		for (auto& open_fd : m_open_files)