Fix download lambda function to take correct param count

This is an emergency fix as a result of something being broken in
master. This is also being pushed straight to master because github is
down and the PR process isn't possible. This commit was reviewed by
@wvu-r7 prior to being pushed.

Author: OJ

lib/rex/post/meterpreter/extensions/stdapi/fs/file.rb

@@ -328,7 +328,7 @@ def File.download_file(dest_file, src_file, opts = nil, &stat)
     continue=false
     tries=false
     tries_no=0
-    stat ||= lambda { }
+    stat ||= lambda { |a,b,c| }
 
     if opts
       continue = true if opts["continue"]