comctl32/toolbar: Erase the background in TOOLBAR_Refresh() when TBSTYLE_TRANSPARENT is present for comctl32 v6.
Comctl32 v6 erases the background when TBSTYLE_TRANSPARENT is present when handling WM_PAINT, not when handling WM_ERASEBKGND. WxWidgets relies on this behavior to draw the toolbar background. Please see https://github.com/wxWidgets/wxWidgets/blob/v2.9.4/src/msw/toolbar.cpp#L1805.
Fix tlReader 10.1.0.2004 toolbar broken rendering after 5e70fef5. After the commit, the comctl32 v6 version is properly reported and wxWidgets decides to use a comctl32 v6 specific code path.