BusesTrace.cmd fails in WinRE

When running under WinRE BusesTrace.cmd fails on this line:
https://github.com/microsoft/busiotools/blob/master/usb/tracing/BusesTrace.cmd#L37

I believe it might be ok to relax the `if` statement below and collect remainder of the log rather than fail. Or perhaps only restrict it to failure of `FIND` rather than both `FIND` and `WHOAMI`