fix: preload extension klasses during bootstrap

Author: dledda-r7

lib/msf/base/sessions/meterpreter.rb

@@ -138,6 +138,7 @@ def shell_init
   end
 
   def load_embedded_extensions
+    Rex::Post::Meterpreter::ExtensionMapper.get_extension_klasses
 
     # First of all, let's see if we have stdapi.
     commands = self.core.get_loaded_extension_commands('stdapi')