Broken page formatting in file index

Formatting of HTML page with file index become broken when a length of filename is more than 51 symbol.

Screenshot: https://yadi.sk/i/dd29ZVEWsXjZE

As a possible solution we can cut filename in dp->d_name when it's length is more than 51 symbols. https://github.com/reyk/httpd/blob/master/httpd/server_file.c#L510 If you have no objections I'll make a patch.