Error 500 for code browsing if README.md contains syntax error
Created by: TomiS
How to reproduce:
Add a following code example in your README.md
```yml
and gain
ClassNotFound: no lexer for alias 'yml' found
which causes Error 500 in user interface.
Of course, the correct name for the lexer should be yaml but even if there's even more horrible errors in README file, Gitlab should fallback more nicely than crashing the whole site with error 500.