Fixed x64 application termination after exceptions in a file dialog callback.

Fixed x64 application termination after exceptions in a file dialog callback.

Since Windows 7 exceptions thrown in a file dialog callback (possibly by third-party utilities) aren't swallowed anymore. Make use of SetProcessUserModeExceptionPolicy (available in Windows 7 SP1) to temporarily restore the old behaviour and prevent the crashing (or summoning of the Program Compatibility Assistant) of an x64 application.

Closes #13674.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69908 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775