Problem:
On running `zig fmt` manually, the on_lines callback and the
server both detach (for some reason), and both of them call
`clear()`. This fixes it, otherwise the second one to detach
has an error in `reset_timer` since the bufstate doesn't exist
Solution:
* exit early in clear if `bufstates[bufnr]` is nil
* set bufstatte.enabled to true on reload instead of making bufstate nil
fa0a25dcb3