#20 use with roundcube-0.9.2

[_GW]

Had problems seeing a white page after updating to RC-0.9.2. (from pre 0.9)
I guess it was related to: https://sourceforge.net/p/rcubevacation/discussion/997972/thread/09d1e9f4#4361

google gave me this:
https://github.com/gianlucagiacometti/roundcube-forward/issues/1

made some modifications to lib/virtual.class.php and created a patch. Hope it works for everyone!
this is my first patch ever - hope it works!

thanks for this great plugin!