Sage cannot compile, when there is an empty sagesilent or sageblock

The following latex code will fail with the following fail.

```
\begin{sagesilent}

\end{sagesilent}
```

```
File "main.sagetex.sage.py", line 32
    except:
    ^
IndentationError: expected an indented block
```

To reproduce:
Create a .tex document and include the sagetex package.
Then add the codeblock above and run

```
pdflatex main.tex
sage main.sagetex.sage
```