Set wxDidCreatePaintDC to true even if we reused a cached wxPaintDC.

Set wxDidCreatePaintDC to true even if we reused a cached wxPaintDC.

Reusing a cached wxPaintDC should count as painting the window, otherwise we
could call DefWindowProc(WM_PAINT) if WM_PAINT was generated from inside
EVT_PAINT handler (e.g. by calling wxWindow::Update()) and this validated the
entire window and no painting was really done.

In particular this fixes redrawing of wxStyledTextCtrl which does call
Update() (completely unnecessarily AFAICS) from its EVT_PAINT handler when it
wants to fully refresh itself.

Closes #13345.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68337 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775