allow detection of filetype if multiple filetypes are declared

not sure if this is the best approach (finding the first suitable file type and using that), but I imagine there's a lot more involved if we wanted to really support multiple file types (eg: html + css), so this at least works with a single type.

Also, I'm not sure if there's a better way to define the found_type variable (not sure if vim has a boolean type). Feel free to correct this code as you see fit.