fix(linematch): initialize array

gsrc/nvim/linematch.c: In function ‘try_possible_paths’:
gsrc/nvim/linematch.c:204:35: warning: ‘from_vals’ may be used uninitialized [-Wmaybe-uninitialized]
  204 |       size_t unwrapped_idx_from = unwrap_indexes(from_vals, diff_len, ndiffs);
      |                                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~