Land rapid7#4917, @hmoore-r7 avoid another payload size recalc

Author: Brent Cook

lib/msf/core/payload_set.rb

@@ -88,7 +88,7 @@ def recalculate
 
       # Cache the payload's size
       begin
-        sizes[name] = p.new.size
+        sizes[name] = p.cached_size || p.new.size
       # Don't cache generic payload sizes.
       rescue NoCompatiblePayloadError
       end