Move argument check so that too many arguments does not panic.
Move argument check so that too many arguments does not panic.

Fixes #95

lotrfan/go-socket.io,1lann/go-socket.io,lunixbochs/go-socket.io,mzgnr/go-socket.io,gsaqui/go-socket.io,xtgxiso/go-socket.io,mzgnr/go-socket.io,wubin1989/go-socket.io,wubin1989/go-socket.io,zhouhui8915/go-socket.io,vinnitu/go-socket.io,xtgxiso/go-socket.io,lotrfan/go-socket.io,mzgnr/go-socket.io,1lann/go-socket.io,xtgxiso/go-socket.io,zhouhui8915/go-socket.io,1lann/go-socket.io,lunixbochs/go-socket.io,gsaqui/go-socket.io,gsaqui/go-socket.io,lunixbochs/go-socket.io,lotrfan/go-socket.io,zhouhui8915/go-socket.io