fix: prevent panic when restarting crashed worker (#49)

testdata/die.php

@@ -0,0 +1,9 @@
+<?php
+
+do {
+    $ok = frankenphp_handle_request(function () use ($i): void {
+        echo 'Hello, world';
+    });
+
+    die('Hello');
+} while ($ok);

worker.go

@@ -74,6 +74,7 @@ func startWorkers(fileName string, nbWorkers int) error {
 
 				// TODO: make the max restart configurable
 				if _, ok := workersRequestChans.Load(absFileName); ok {
+					workersReadyWG.Add(1)
 					l.Error("unexpected termination, restarting", zap.String("worker", absFileName))
 				} else {
 					break

worker_test.go

@@ -41,6 +41,14 @@ func TestWorker(t *testing.T) {
 	}, &testOptions{workerScript: "worker.php", nbWorkers: 1, nbParrallelRequests: 1})
 }
 
+func TestWorkerDie(t *testing.T) {
+	runTest(t, func(handler func(http.ResponseWriter, *http.Request), _ *httptest.Server, i int) {
+		req := httptest.NewRequest("GET", "http://example.com/die.php", nil)
+		w := httptest.NewRecorder()
+		handler(w, req)
+	}, &testOptions{workerScript: "die.php", nbWorkers: 1, nbParrallelRequests: 10})
+}
+
 func ExampleServeHTTP_workers() {
 	if err := frankenphp.Init(
 		frankenphp.WithWorkers("worker1.php", 4),