perf(filetype): skip contents check in `match()` if there is no contents (#29596)

Problem: `vim.filetype.match()` tries to match on contents even if there
  is no contents (empty buffer or `{''}` explicit contents).
  This results in extra avoidable execution duration for cases.
  It matters, for example, when trying to match filetype based solely
  on file name (which still needs `contents` or `buf` to properly match
  earlier in the code path).

Solution: skip matching based solely on contents if it is `{''}`. This
  works because:
    - Matching solely on content is done after any user-configured
      `vim.filetype.add()` hooks.
    - All default matching on content might depend on supplied path
      *only* if there is non-empty content (like in
      `require('vim.filetype.detect').match_from_hashbang()`).

0 files changed, 0 insertions, 0 deletions