Fix match

Author: Takahiro-Yoko

modules/exploits/linux/http/empire_skywalker.rb

@@ -146,8 +146,9 @@ def get_staging_key
           'uri'       => normalize_uri(target_uri.path, 'download/python/')
         })
         return unless res and res.code == 200
-        staging_key = /IV\+\'(.*)\'\.encode/.match(res.body)[1].bytes
-        return staging_key
+        match = /IV\+\'(.*)\'\.encode/.match(res.body)
+        return match[1].bytes if match
+        return
     end
 
     # STAGE0_URI resource requested by the initial launcher