Avoid using buffer of already deallocated string in wxHTMLDataObject.

Ensure that the temporary string inside which the pointer returned by
utf8_str() may point remains alive for long enough.

Closes #15279.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74429 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Don't pretend that wxAnyButton::SetBitmap() supports invalid bitmaps.

Because it doesn't under MSW.

See #13569.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74430 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775