Fix possible crashes on OCSP request timeout (#12982)

* Fix possible crashes on OCSP request timeout

* Acquire lock in do_io_shutdown

Author: maskit

src/proxy/FetchSM.cc

@@ -61,6 +61,7 @@ FetchSM::cleanUp()
   }
 
   if (http_vc) {
+    http_vc->do_io_shutdown(IO_SHUTDOWN_READWRITE);
     http_vc->do_io_close();
   }
   free_MIOBuffer(req_buffer);

src/proxy/PluginVC.cc

@@ -397,6 +397,8 @@ PluginVC::do_io_shutdown(ShutdownHowTo_t howto)
   ink_assert(!closed);
   ink_assert(magic == PluginVCMagic_t::ALIVE);
 
+  SCOPED_MUTEX_LOCK(lock, mutex, this_ethread());
+
   switch (howto) {
   case IO_SHUTDOWN_READ:
     read_state.shutdown = true;