typefind: Expand the search range for HLS detection

typefind: Expand the search range for HLS detection

HLS files can have arbitrary extra tags in them, and
those can be quite long lines. We need to search
further than 256 bytes sometimes just to get past the
first few lines of the file. Make the limit 4KB,
which matches a typical input block size and should
hopefully cover every crazy input.

https://bugzilla.gnome.org/show_bug.cgi?id=780559