srmspacemanager: catch and ignore SQL exception on error handling path w...

...hen processing PoolMgrSelectWritePool on reply from PoolManager

In the previous version of selectPool the srmspace file has always been
defined (even if id had no pnfsid associdated). Recent changes introduced
better separation of handling messages to PoolManager and from PoolManager.
In case of reply only error handling part is needed (nullify pnfsid of
srmspacefile record).

Ticket: 8087
Acked-by:
Request: 2.7
Require-book: no
Require-notes: no