Do not crash when test run in child process ends unexpectedly and --log-junit is used

Author: kubawerlos

src/Logging/JUnit/JunitXmlLogger.php

@@ -202,7 +202,7 @@ public function testPrepared(): void
      */
     public function testFinished(Finished $event): void
     {
-        if ($this->preparationFailed) {
+        if (!$this->prepared || $this->preparationFailed) {
             return;
         }