🥅 Work around JRuby IO#close thread-safety issue

In CRuby, the same IO object generally can't be closed concurrently from
multiple threads thanks to the GVL.  But also, it checks and double
checks whether or not the IO object has already been closed around
critical sections, and simply returns if it's already been closed.

JRuby seems to handle concurrent `IO#close` similarly to if the losing
thread were trying to read or write.  So it can easily be triggered into
raise an IOError with "closed stream".

Author: nevans

lib/net/imap.rb

@@ -1215,10 +1215,20 @@ def disconnect(timeout: nil)
         @sock.to_io.shutdown
       rescue Errno::ENOTCONN
         # ignore `Errno::ENOTCONN: Socket is not connected' on some platforms.
+      rescue IOError => e
+        # IO#close should be safe against being closed by another thread, but
+        # JRuby raises this error sometimes.
+        raise unless e.message == "closed stream"
       rescue Exception => e
         @receiver_thread.raise(e) unless in_receiver_thread
       end
-      @sock.close
+      begin
+        @sock.close
+      rescue IOError => e
+        # IO#close should be safe against being closed by another thread, but
+        # JRuby raises this error sometimes.
+        raise unless e.message == "closed stream"
+      end
       @receiver_thread.join(timeout) unless mon_owned? || in_receiver_thread
       raise e if e
     ensure