azureblob: fix SAS URL support - fixes #2969

This was broken accidentally in 5d1d93e163 as part of #2654

backend/azureblob/azureblob.go

@@ -392,6 +392,7 @@ func NewFs(name, root string, m configmap.Mapper) (fs.Fs, error) {
 				return nil, errors.New("Container name in SAS URL and container provided in command do not match")
 			}
 
+			f.container = parts.ContainerName
 			containerURL = azblob.NewContainerURL(*u, pipeline)
 		} else {
 			serviceURL = azblob.NewServiceURL(*u, pipeline)