ensure os_flavor can be supplied for no Windows OS

Author: jmartin-tech

lib/msf/core/db_manager/host.rb

@@ -221,7 +221,9 @@ def report_host(opts)
         os_name, os_flavor = split_windows_os_name(opts[:os_name])
         opts[:os_name] = os_name if os_name.present?
         if opts[:os_flavor].present?
-          opts[:os_flavor] = os_flavor + opts[:os_flavor]
+          if os_flavor.present? # only prepend if there is a value that needs it
+            opts[:os_flavor] = os_flavor + opts[:os_flavor]
+          end
         else
           opts[:os_flavor] = os_flavor
         end