Error handling now done correctly

[Viraj Indasrao]

gorbac/permission.go

Line 32 in a989d0e

 func (p *StdPermission) Match(a Permission) bool { 

api:runtime error: invalid memory address or nil pointer dereference
github.com/mikespook/gorbac/permission.go:33
github.com/mikespook/gorbac/role.go:53
github.com/mikespook/gorbac/rbac.go:199
github.com/mikespook/gorbac/rbac.go:194
github.com/mikespook/gorbac/helper.go:78

[Xing]

Could you give me more details? Thanks!