Avoid sending headers twice on write error (#194)

* Avoid sending headers twice on write error

* Format only

---------

Co-authored-by: Rob Bygrave <[email protected]>

Author: SentryMan

avaje-jex/src/main/java/io/avaje/jex/core/ExceptionManager.java

@@ -56,6 +56,11 @@ private void unhandledException(JdkContext ctx, Exception e) {
   }
 
   private void defaultHandling(JdkContext ctx, HttpResponseException exception) {
+    if (ctx.responseSent()) {
+      // if already sent headers, can't send again
+      return;
+    }
+
     ctx.status(exception.status());
     var jsonResponse = exception.jsonResponse();
     if (exception.status() == HttpStatus.FOUND_302.status()) {