Syntax errors in playground sometimes trigger `ENOENT: /static/playground.res, no such file or directory` error

[mediremi]

When using v12.0.0-alpha.14 on the playground, syntax errors sometimes trigger the error ENOENT: /static/playground.res, no such file or directory.

I haven't been able to reproduce this issue in v12.0.0-alpha.13 or earlier versions.

---

By setting the --debug-info jsoo flag, I've narrowed it down to protect_refs from misc.ml:

rescript/compiler/ext/misc.ml

Lines 41 to 52 in 3079bdb

	let protect_refs =
	let set_refs l = List.iter (fun (R (r, v)) -> r := v) l in
	fun refs f ->
	let backup = List.map (fun (R (r, _)) -> R (r, !r)) refs in
	set_refs refs;
	match f () with
	| x ->
	set_refs backup;
	x
	| exception e ->
	set_refs backup;
	raise e

Only two functions call protect_refs: Env.without_cmis and Warnings.without_warnings