SoapySDRServer unexpectedly terminates

[eblot]

See initial bug report and GDB backtrace from pothosware/SoapyRemote#44

Maybe the destructor attempts to clean up IIO instances which have already been destroyed when the client died?

[guruofquality]

The closeStream hook needs to cleanup anything that may have been left active by activateStream(), right now it looks like closeStream() crashes if deactivate was not called. closeStream should be able to clean up nicely regardless.