No log region means full logregion

Good catch by Coverity CID#469254

src/fellow_log.c

@@ -2363,7 +2363,8 @@ logbuffer_prep_dskreqs(struct fellow_logbuffer *lbuf, unsigned urgent)
 	 * XXX is 25% a good measure?
 	 */
 	if (lbuf->dskreqs_mem.reqs.magic == 0 &&
-	    (lbuf->logreg->free_n * 4 < lbuf->logreg->space ||
+	    (lbuf->logreg == NULL ||
+	     lbuf->logreg->free_n * 4 < lbuf->logreg->space ||
 	     lbuf->logreg->free_n < lbuf->n * 4)) {
 		BUDDY_REQS_INIT(&lbuf->dskreqs_mem, lbuf->membuddy);
 		BUDDY_REQS_PRI(&lbuf->dskreqs_mem.reqs, FEP_MEM_LOG);