Fix uncommentout error in treesitter

[yuki-yano]

When uncommenting while applying treesitter, an error occurred when vim.treesitter.highlighter.hl_map was nil. Fixed it so that if it is nil, it is judged to be in a comment and processed.

[tyru]

Duplicate #171

Thanks for report. And sorry for late reply.

[Ttayu]

@tyru The following errors continue to occur with #171

[Vim(if):E5108: Error executing lua ...ka/.cache/dein/repos/github.com/tyru/caw.vim/lua/caw.lua:26: attempt to index field 'hl_map' (a nil value)^@stack traceback:^@^I...ka/.cache/dein/repos/github.com/tyru/c
aw.vim/lua/caw.lua:26: in function 'has_syntax'^@^I[string "luaeval()"]:1: in main chunk]::[function caw#keymapping_stub[78]..37[3]..42[2]..39[2]..29[4]..40, line 9]

but, no error occurs in this PR.

[mpg-kyosuke-takayama]

same here