Check if it's valid event handle. This will get rid of run time exception.

This commit was SVN r15154.

opal/util/output.c

@@ -293,7 +293,8 @@ void opal_output_close(int output_id)
             closelog();
         }
 #elif defined(__WINDOWS__)
-        DeregisterEventSource(info[output_id].ldi_syslog_ident);
+        if(info[output_id].ldi_syslog_ident != NULL)
+            DeregisterEventSource(info[output_id].ldi_syslog_ident);
 #endif
     }