Tracekit bug fix

[BenjaminHarding]

Fixes a bug where our version of tracekit wouldn't go past the computeStackTraceFromStackProp due to it passing back a truthy value.

[UberMouse]

I have no idea what this change does. But I assume it's fine

[BenjaminHarding]

Let me explain then. In tracekit there are a number of different ways to compute the stacktrace depending on the browser/properties on the exception.

All of these computeStackTraceFrom[X] methods are called in order when they continue to return falsely values.

The bug comes from a previous update changing one of the computeStackTrace methods to return a object instead of falsely, thus breaking it.