Handle MathJax errors and exceptions properly
Handle MathJax errors and exceptions properly

When an exception is thrown during the rendering process, Mathoid just
dies with an unhandled exception. Likewise, if MathJax-node produces an
error (by way of setting data.errors), we would return a 200 code with
an empty body. This commit fixes both of these issues.

Change-Id: I1e226bf7847cc58c51840d1d47d6fb173fcfc25a

wikimedia/mathoid,wikimedia/mathoid,wikimedia/mathoid,physikerwelt/mathoid-server,physikerwelt/mathoid-server,wikimedia/mathoid,physikerwelt/mathoid-server