Azurite doesn't support Create Blob with blob name that is empty string

**Error Description:**
In Azure, it will create blob successfully when create blob with blob name that is empty string.
But in Azurite, it will return an error as following in this case:

**To Reproduce**
Please run the demo code as following:
```
import {
BlobServiceClient
} from "@azure/storage-blob";

async function main(){
const blobServiceClient = await BlobServiceClient.fromConnectionString("");
const containerClient=await blobServiceClient.getContainerClient("");
const appendBlobClient = await containerClient.getAppendBlobClient("");
}

main();
```

**Error Track:**
1. When send request, Azurite will construct a pattern by request to match the corresponding handler method. it will construct a pattern(/container) without blob when use a blob name of empty string to create blob
[https://github.com/Azure/Azurite/blob/master/src/blob/middlewares/blobStorageContext.middleware.ts#L80](https://github.com/Azure/Azurite/blob/master/src/blob/middlewares/blobStorageContext.middleware.ts#L80)

2. When use the pattern to match handler method, it doesn't match the blob create handler method because the blob create handler method need a pattern like "container/blob".
[https://github.com/Azure/Azurite/blob/master/src/blob/generated/middleware/dispatch.middleware.ts#L105](https://github.com/Azure/Azurite/blob/master/src/blob/generated/middleware/dispatch.middleware.ts#L105)
[https://github.com/Azure/Azurite/blob/master/src/blob/generated/artifacts/specifications.ts#L2027](https://github.com/Azure/Azurite/blob/master/src/blob/generated/artifacts/specifications.ts#L2027)

**Expected Behavior**
When create blob with blob name that is empty string in azurite, it can create blob successfully.

@jongio for notification.