Fix UnboundLocalError when tidy selected HTML content

If I select some HTML content and run tidy command, I will get the following error.
Traceback (most recent call last):
  File ".\sublime_plugin.py", line 362, in run_
  File ".\html_tidy.py", line 339, in run
UnboundLocalError: local variable 'deselect_flag' referenced before assignment
Merge pull request #33 from longhua/patch-1

Fix UnboundLocalError when tidy selected HTML content