Adjust error handling for extension enumeration

Make the catch case more generic for when the target doesn't support the
command for extension enumeration. This supports more than just windows
now.

lib/rex/post/meterpreter/client_core.rb

@@ -53,13 +53,11 @@ class ClientCore < Extension
     # No response?
     if response.nil?
       raise RuntimeError, "No response was received to the core_enumextcmd request.", caller
-    elsif response.result == 50
+    elsif response.result != 0
       # This case happens when the target doesn't support the core_enumextcmd message.
       # If this is the case, then we just want to ignore the error and return an empty
       # list. This will force the caller to load any required modules.
       return []
-    elsif response.result != 0
-      raise RuntimeError, "The core_enumextcmd request failed with result: #{response.result}.", caller
     end
 
     commands = []