properly free memory/close fd upon errors (Thanks xeen)

Found with the static analyzer cppcheck

src/util.c

@@ -374,11 +374,13 @@ char *store_restart_layout() {
         if (n == -1) {
             perror("write()");
             free(filename);
+            close(fd);
             return NULL;
         }
         if (n == 0) {
             printf("write == 0?\n");
             free(filename);
+            close(fd);
             return NULL;
         }
         written += n;