tree: gracefully handle empty dirs

When no devices are present, /sys/class/nvme and
/sys/class/nvme-subsystem directories may not exist. scandir returns
-1 with errno set to ENOENT.

nvme_scan treats this as a fatal error instead it should just ignore it.
There is just nothing to scan.

This fixes the python-create-ctrl-object and python-sigsegv-during-gc tests
that fail when no NVMe devices are present in the test environment.

Signed-off-by: Daniel Wagner <[email protected]>

Author: igaw

libnvme/src/nvme/tree.c

@@ -355,7 +355,7 @@ int nvme_scan(const char *config_file, struct nvme_global_ctx **ctxp)
 		return -ENOMEM;
 
 	ret = nvme_scan_topology(ctx, NULL, NULL);
-	if (ret)
+	if (ret && ret != -ENOENT)
 		goto err;
 	if (config_file) {
 		ret = nvme_read_config(ctx, config_file);