chore(init.lua): do not invoke DoomStarted while PackerSync is running

When running doom for the first time (or after ~/.local/share/nvim/site
is cleaned) doom will bootstrap itself by calling packer.sync().
However that happens asynchronously, so do not call DoomStarted in this
case: doom is not ready yet.

This will allow to safely run the following command to synchronize doom
config with packages:
```
nvim --headless --cmd "autocmd User PackerComplete quitall" --cmd "autocmd User DoomStarted PackerSync"
```

Previously such a command wouldn't have been safe on initial run due to
the implicit packer.sync: 2 packer syncs running at the same time would
show a lot of lua module errors about modules not found, it is best
avoided.
On subsequent runs it would've been safe but it is useful to have a
single command to run that is always safe.

This should also make it possible to use a similar command in a CI to
wait for the installation of packages and then test that the doom config
works.

Signed-off-by: Edwin Török <edwin@etorok.net>

Author: edwintorok

lua/doom/core/init.lua

@@ -71,8 +71,10 @@ modules.try_sync()
 profiler.stop("framework|doom.core.modules")
 
 -- Execute autocommand for user to hook custom config into
-vim.api.nvim_exec_autocmds("User", {
-  pattern = "DoomStarted",
-})
+if not modules._needs_sync then
+  vim.api.nvim_exec_autocmds("User", {
+    pattern = "DoomStarted",
+  })
+end
 
 -- vim: fdm=marker