fix(highlight): return false when the capture is not a comment

Fixes #301

Author: geoffreylefebvre

lua/todo-comments/highlight.lua

@@ -64,6 +64,7 @@ function M.is_comment(buf, row, col)
         return true
       end
     end
+    return false
   else
     local win = vim.fn.bufwinid(buf)
     return win ~= -1