logging: allow inode/offset params to be NULL

Not all callers of virLogManagerDomainOpenLogFile will
care about getting the current inode/offset, so we should
allow those parameters to be NULL
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

src/logging/log_manager.c

@@ -196,7 +196,9 @@ virLogManagerDomainOpenLogFile(virLogManagerPtr mgr,
         goto cleanup;
     }
 
+    if (inode)
         *inode = ret.pos.inode;
+    if (offset)
         *offset = ret.pos.offset;
 
     rv = fdout[0];