✅ Fix FakeServer error handling on LOGOUT

I haven't traced down what's _causing_ the error.  It seems like the
socket is closed prematurely, so probably a race condition?  At any
rate, it should be safe to simply warn about the exception rather than
crash.

Author: nevans

test/net/imap/fake_server/command_router.rb

@@ -60,7 +60,7 @@ def handler_for(command)
       rescue IOError
         # TODO: fix whatever is causing this!
         warn "connection issue after bye but before LOGOUT could complete"
-        if $!.respond_to :detailed_message
+        if $!.respond_to? :detailed_message
           warn $!.detailed_message highlight: true, order: :bottom
         else
           warn $!.full_message     highlight: true, order: :bottom