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

[Alexnortung]

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

[dimpase]

thanks for the report, and please feel free to provide a PR to fix this issue.