Fix bug in WindowsBalloonTip

[Chronial]

icon_path_name is not defined. So passing an invalid icon file will raise an error about that instead of the expected Exception:

Traceback (most recent call last):
  File ".\win-popup.py", line 6, in <module>
    app_name='sync-seedbox', timeout=10)
  File "C:\Tools\Python35\lib\site-packages\plyer\platforms\win\libs\balloontip.py", line 145, in balloon_tip
    WindowsBalloonTip(**kwargs)
  File "C:\Tools\Python35\lib\site-packages\plyer\platforms\win\libs\balloontip.py", line 91, in __init__
    format(icon_path_name))
NameError: name 'icon_path_name' is not defined

[KeyWeeUsr]

@Chronial Thanks! It's basically from 1d7fb1f where the name was removed, but apparently not updated(typo). The else part of that block should load just the default application icon:

IDI_APPLICATION MAKEINTRESOURCE(32512) | Default application icon.
(source)