fix "reverse range in character class" error (#818)
fix "reverse range in character class" error (#818)

Summary: fix "reverse range in character class" error when triggering autocommand for a buffer with a name containing reverse regex character class (range of chars in square braces like `[a-z]`, but with the right side < left side: `[z-a]`) as a part of a name.
In particular triggers for luadev buffer which has a default name `[nvim-lua]`
Yggdroot/LeaderF,Yggdroot/LeaderF,Yggdroot/LeaderF