fix(lsp): only fire LspDetach for attached buffers (#22468)

If the LSP server fails to start then the client never initializes and
thus never calls its on_attach function and an LspAttach event is
never fired. However, the on_exit function still fires a LspDetach
event, so user autocommands that attempt to "clean up" in LspDetach may
run into problems if they assume that the buffer was already attached.

The solution is to only fire an LspDetach event if the buffer was
already attached in the first place.

runtime/lua/vim/lsp.lua

@@ -1155,14 +1155,19 @@ function lsp.start_client(config)
       pcall(config.on_exit, code, signal, client_id)
     end
 
+    local client = active_clients[client_id] and active_clients[client_id]
+      or uninitialized_clients[client_id]
+
     for bufnr, client_ids in pairs(all_buffer_active_clients) do
       if client_ids[client_id] then
         vim.schedule(function()
-          nvim_exec_autocmds('LspDetach', {
-            buffer = bufnr,
-            modeline = false,
-            data = { client_id = client_id },
-          })
+          if client and client.attached_buffers[bufnr] then
+            nvim_exec_autocmds('LspDetach', {
+              buffer = bufnr,
+              modeline = false,
+              data = { client_id = client_id },
+            })
+          end
 
           local namespace = vim.lsp.diagnostic.get_namespace(client_id)
           vim.diagnostic.reset(namespace, bufnr)
@@ -1178,8 +1183,6 @@ function lsp.start_client(config)
     -- Schedule the deletion of the client object so that it exists in the execution of LspDetach
     -- autocommands
     vim.schedule(function()
-      local client = active_clients[client_id] and active_clients[client_id]
-        or uninitialized_clients[client_id]
       active_clients[client_id] = nil
       uninitialized_clients[client_id] = nil