Fix when() clause cutting stack traces when filtering doesn't succeed (fix for 46661...

Fix when() clause cutting stack traces when filtering doesn't succeed (fix for 46661) (#4328)

* * [exceptions] When encountering a filter (when) clause, don't setup the stack trace before we know if the filter is going to work. Otherwise, any exception that isn't blocked by the when clause will have its stack trace cut at the point of the parent of the function containing the when clause
* Fixes https://bugzilla.xamarin.com/show_bug.cgi?id=46661

* + Added test case for bug 46661