Add null check in NetworkStateNotifier::updateStateWithoutNotifying

https://bugs.webkit.org/show_bug.cgi?id=259163
rdar://111926368

Reviewed by Brent Fulgham.

Crash logs indicate m_store can be null and it crashes when it is.
In NetworkStateNotifier::startObserving we early return if it's null.
This adds another early return.

* Source/WebCore/platform/network/mac/NetworkStateNotifierMac.cpp:
(WebCore::NetworkStateNotifier::updateStateWithoutNotifying):

Canonical link: https://commits.webkit.org/266011@main

Source/WebCore/platform/network/mac/NetworkStateNotifierMac.cpp

@@ -35,6 +35,9 @@ namespace WebCore {
 
 void NetworkStateNotifier::updateStateWithoutNotifying()
 {
+    if (!m_store)
+        return;
+
     auto key = adoptCF(SCDynamicStoreKeyCreateNetworkInterface(0, kSCDynamicStoreDomainState));
     auto propertyList = dynamic_cf_cast<CFDictionaryRef>(adoptCF(SCDynamicStoreCopyValue(m_store.get(), key.get())));
     if (!propertyList)