Fix datastore to validate options w/o a default

Options without a default were not pulled into the `@options` hash and
therefore were not used to validate options on assignment.

I am not entirely sure how this fix works, since it would seem that
non-override options would not get pulled in if an option was first set
in the global datastore. However, a previous value does not get
overridden and new values are validated. Anything further is merely
speculation on my part.

lib/msf/core/data_store.rb

@@ -75,8 +75,7 @@ class DataStore < Hash
   #
   def import_options(options, imported_by = nil, overwrite = false)
     options.each_option do |name, opt|
-      # Skip options without a default or if is already a value defined
-      if !opt.default.nil? && (self[name].nil? || overwrite)
+      if self[name].nil? || overwrite
         import_option(name, opt.default, true, imported_by, opt)
       end
     end