fix(lsp): process semantic tokens LspNotify callback only when attached #40450

Problem: LspNotify will fire for any attached client. If there's at
least two clients where one has semantic tokens enabled and one that
doesn't, the disabled one will get the LspNotify requests but won't have
a client state.

Solution: Only process LspNotify autocmds if there's a client state to
act on.

Fixes #40448

runtime/lua/vim/lsp/semantic_tokens.lua

@@ -213,6 +213,11 @@ function STHighlighter:new(bufnr)
 
   nvim_on('LspNotify', self.augroup, { buf = self.bufnr }, function(opts)
     local client_id = opts.data.client_id ---@type integer
+
+    if not self.client_state[client_id] then
+      return
+    end
+
     if opts.data.method == 'textDocument/didClose' then
       self:reset(client_id)
     end