pmem2: fix munmap when file mapping fails (posix)

Reservation region should be unmapped only when it wasn't provided
by the config, otherwise the job of cleaning up the reservation is
up to the invoking layer.

src/libpmem2/map_posix.c

@@ -488,8 +488,13 @@ pmem2_map_new(struct pmem2_map **map_ptr, const struct pmem2_config *cfg,
 	ret = file_map(reserv, content_length, proto, flags, map_fd, off,
 			&map_sync, &addr);
 	if (ret) {
-		/* unmap the reservation mapping */
-		munmap(reserv, reserved_length);
+		/*
+		 * unmap the reservation mapping only
+		 * if it wasn't provided by the config
+		 */
+		if (!cfg->reserv)
+			munmap(reserv, reserved_length);
+
 		if (ret == -EACCES)
 			ret = PMEM2_E_NO_ACCESS;
 		else if (ret == -ENOTSUP)