don't invalidate the error ranges for online check syntax when there is no admin
don't invalidate the error ranges for online check syntax when there is no admin

I believe that this can go wrong in the case that you edit a buffer and switch tabs
before drracket fully finishes responding to the edited buffer (due to a queue-callback
that postpones some of the response to editing the buffer) for online expansion.
At least, this is how I guess that the error below happened:

send: target is not an object: #f for method: get-view

 === context ===
/Users/robby/git/exp/plt/collects/racket/private/class-internal.rkt:4602:0: obj-error
/Users/robby/git/exp/plt/collects/drracket/private/module-language.rkt:1485:6: get-box method in .../module-language.rkt:1151:4
/Users/robby/git/exp/plt/collects/drracket/private/module-language.rkt:1397:6: invalidate-online-error-ranges method in .../module-language.rkt:1151:4
/Users/robby/git/exp/plt/collects/drracket/private/module-language.rkt:1387:6: clear-old-error method in .../module-language.rkt:1151:4
/Users/robby/git/exp/plt/collects/drracket/private/module-language.rkt:1177:6: buffer-modified method in .../module-language.rkt:1151:4
/Users/robby/git/exp/plt/collects/mred/private/wx/common/timer.rkt:34:38
/Users/robby/git/exp/plt/collects/mred/private/wx/common/queue.rkt:432:6
/Users/robby/git/exp/plt/collects/mred/private/wx/common/queue.rkt:472:32
/Users/robby/git/exp/plt/collects/mred/private/wx/common/queue.rkt:618:3

mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket