misleading error when specified target is not in config file and config file doesn't have a project scope

[rick]

To reproduce:

Given a config like this: https://gist.github.com/3123721 with no outer project scoping,
Run a setup or deploy specifying a target not in the file. E.g., wd setup --to=staging
The filter to wrap with a project scope fails, but the error message sucks:

Class:0x458dc649: undefined method `[]' for nil:NilClass

         override_project_name! at /Users/grant/.rvm/gems/jruby-1.6.7.2/gems/whiskey_disk-0.6.24/lib/whiskey_disk/config/filters/project_scope_filter.rb:24
                      filter at /Users/grant/.rvm/gems/jruby-1.6.7.2/gems/whiskey_disk-0.6.24/lib/whiskey_disk/config/filters/project_scope_filter.rb:29