Appease Flexelint wrt regions bounds checking

This change should be semantically equivalent, but Flexelint understands
it.

src/fellow_cache.c

@@ -1488,8 +1488,9 @@ fellow_obj_regions(const struct fellow_fd *ffd,
 		CHECK_OBJ(fcsl, FELLOW_CACHE_SEGLIST_MAGIC);
 		CHECK_OBJ_NOTNULL(fdsl, FELLOW_DISK_SEGLIST_MAGIC);
 
-		region[n++] = fdsl->next;
-		assert(n <= FCO_MAX_REGIONS);
+		assert(n < FCO_MAX_REGIONS);
+		region[n] = fdsl->next;
+		n++;
 		fdsl = fcsl->fdsl;
 	}
 	DBG("+seglists %u", n);