pml/ob1: Move sendreq 'error after freed' check to correct location

[Matthew-Whitlock]

It is currently in the path for send requests which have NOT been freed. This moves it to the correct conditional branch. For reference, this change reflects how it is done for recv requests here.

Full disclaimer: I'm only really seeing this give spurious errors when using the resilient OFI btl from PR https://github.com/open-mpi/ompi/pull/13429, but the issue seems to be generic.