blob_size is undefined in baseblobservice

### Which service(blob, file, queue) does this issue concern?
blob

### Which version of the SDK was used? Please provide the output of `pip freeze`.
v2.1.0

### What problem was encountered?
`blob_size` is undefined in line 2212 in `azure-storage-python/azure-storage-blob/azure/storage/blob/baseblobservice.py`

### Have you found a mitigation/solution?
Maybe we also set `blob_size` in the except branch in line 2189 and so we have it defined in both cases.

Note: for table service, please post the issue here instead: https://github.com/Azure/azure-cosmosdb-python.

El error se encuentra en azure-storage-python/azure-storage-blob/azure/storage/blob/baseblobservice.py, alrededor de las líneas 2189-2212. Empieza rastreando cómo se asigna blob_size en las rutas normal y de excepción para la operación de blob indicada. Se considera terminado cuando la operación ya no produce un error de variable no definida al tomar la ruta de excepción.

Escrito por el modelo de indexación a partir del texto del issue.