Start generating guide again for empty profile

We stopped generating guide for empty profile after
1ffbdcd which confused

    if @scap_content.nil? or @scap_content.source.nil?

with

    if self.scap_content.blank? || self.scap_content_profile.blank?

This is partial revert. As well it is anecdotal evidence about
ineffectiveness of peer reviews and merrits of small commits.

app/models/scaptimony/policy.rb

@@ -20,7 +20,7 @@ def assign_assets(a)
     end
 
     def to_html
-      if self.scap_content.blank? || self.scap_content_profile.blank?
+      if self.scap_content.nil? || self.scap_content.source.nil?
         return (_('<h2>Cannot generate HTML guide for %{scap_content}/%{profile}</h2>') %
           { :scap_content => self.scap_content, :profile => self.scap_content_profile }).html_safe
       end