additional case handling if base_url is defined, but empty.
solves problem with redirecting to anoer app described here
https://groups.google.com/forum/?fromgroups=#!topic/chicagoboss/LXR_TI6nZQk
WebSockets: callback arity fix for service handler

Related to the changes made in c1bdf0223c.
Merge pull request #321 from ztmr/master

WebSockets: callback arity fix for service handler
Merge pull request #327 from danikp/fix_app_redirect

additional case handling if base_url is defined, but empty.