Land rapid7#4173, @wchen-r7's fix for SMB find_first

* Fixes rapid7#4119, SMB find_first("\\*") does not return accurate results
* It missed initialization of sid

Author: jvazquez-r7

lib/rex/proto/smb/client.rb

@@ -1872,6 +1872,7 @@ def queryfs_fs_attribute
 
   # Enumerates a specific path on the mounted tree
   def find_first(path)
+    sid = nil
     files = { }
     parm = [
       26,  # Search for ALL files