Fix bypassuac_injection_winsxs for x64

Tested on Windows 8.1, prior to these chagnes the bad railgun definition
would cause the session to crash.

modules/exploits/windows/local/bypassuac_injection_winsxs.rb

@@ -276,8 +276,8 @@ class MetasploitModule < Msf::Exploit::Local
       andOperation = fileAttributes & client.railgun.const("FILE_ATTRIBUTE_DIRECTORY")
       if andOperation
         # Removes the remainder part composed of 'A' of the path and the last null character
-        normalizedData = findFileData[fileNamePadding, fileNamePadding + maxPath].split('AAA')[0]
-        path = "#{payload_filepath}\\#{normalizedData[0, normalizedData.length - 1]}"
+        normalizedData = findFileData[fileNamePadding, fileNamePadding + maxPath].split("\x00", 2).first
+        path = "#{payload_filepath}\\#{normalizedData}"
         directoryNames.push(path)
       end