guess_lexer_for_filename can also raise a TypeError
    
    Fixes the backstrace received by email
    ````
      File "/usr/lib/python2.7/site-packages/pagure/ui/repo.py", line 379, in view_file
        content.data
      File "/usr/lib/python2.7/site-packages/pygments/lexers/__init__.py", line 183, in guess_lexer_for_filename
        rv = lexer.analyse_text(_text)
      File "/usr/lib/python2.7/site-packages/pygments/util.py", line 120, in text_analyse
        return min(1.0, max(0.0, float(rv)))
    TypeError: float() argument must be a string or a number
    
    ````