[BUG]CatchErrors in LogConverter - stackframe can be null and is not treated in code

[ionutcalin]

In CatchErrors method of LogConverter for Serilog you are trying to get first frame from the stacktrace of each exception (and also for all inner exceptions).
The problem is that the frame is not tested for null and it will throw an exception when trying to obtain the fileName, method etc.

To reproduce is very simple. In user code (in a controller for instance) just add this line:
throw new ApplicationException("lorem...", new ApplicationException("ipsum"));

Obs.: For the inner exception the stack trace will have no frames as it was issued in the same context like the outer exception and this will cause the LogConverter to fail on CatchErrors methon when treating the inner exceptions