LibWeb: Do not dereference empty Optional in ReadableStream::visit_edges

There are quite a few steps between a ReadableStream being created and
its controller being set. If GC occurs between those points, we will
have an empty Optional in ReadableStream::visit_edges. Seen on YouTube.

1 files changed, 2 insertions, 1 deletions

diff --git a/Userland/Libraries/LibWeb/Streams/ReadableStream.cpp b/Userland/Libraries/LibWeb/Streams/ReadableStream.cpp
index ef321ad4cb..de150649c6 100644
--- a/Userland/Libraries/LibWeb/Streams/ReadableStream.cpp
+++ b/Userland/Libraries/LibWeb/Streams/ReadableStream.cpp
@@ -108,7 +108,8 @@ JS::ThrowCompletionOr<void> ReadableStream::initialize(JS::Realm& realm)
 void ReadableStream::visit_edges(Cell::Visitor& visitor)
 {
     Base::visit_edges(visitor);
-    m_controller->visit([&](auto& controller) { visitor.visit(controller); });
+    if (m_controller.has_value())
+        m_controller->visit([&](auto& controller) { visitor.visit(controller); });
     visitor.visit(m_stored_error);
     visitor.visit(m_reader);
 }