Errors and fatal error when closing citr windows

[ThBuettner]

I have obeserved that citr does not respond well when it is invoked but not citation is inserted. In those cases, pressing "Cancel" results in:
Error: User cancel
Called from: shiny::runApp(app, port = port, launch.browser = viewer)
When instead one clicks on the close box at the upper right corner, the R Session is aborted bedause of a fatal error.
I also observed (sometimes) that the library file specified in the YAML header is not found. It seems that knitr needs to be executed first.
Thanks for your attention and for an otherwise very helpful addin.

Thomas