comctl32/listview: Compare item text on insert depending on A/W message

[Nikolay Sivov]

This is a regression since 2829c5fd1e4d36274031c5e78543b4ec741ba8b2
I suppose. Previously comparison was performed always on W strings,
after set_main_item() which does conversion if needed. I copied this code
without respect to isW flag.

Bug reported as http://bugs.winehq.org/show_bug.cgi?id=20742.
Thanks, Satoshi Nakamoto for spotting this.

Changelog:
    - Compare item text on insert depending on A/W message