Cherry-pick 270295@main (6fa5837). https://bugs.webkit.org/show_bug.c…

…gi?id=264380

    nullptr crash in EventPath::eventTargetRespectingTargetRules via EventPath::buildPath
    https://bugs.webkit.org/show_bug.cgi?id=264276
    <rdar://117902151>

    Reviewed by Chris Dumez.

    Add a nullptr check where the crash occurs. Also add a debug assert since this node
    should never be nullptr in theory.

    * Source/WebCore/dom/EventPath.cpp:
    (WebCore::EventPath::buildPath):

    Canonical link: https://commits.webkit.org/270295@main

Source/WebCore/dom/EventPath.cpp

@@ -133,6 +133,9 @@ void EventPath::buildPath(Node& originalTarget, Event& event)
         if (!shouldEventCrossShadowBoundary(event, shadowRoot, originalTarget))
             return;
         node = shadowRoot.host();
+        ASSERT(node);
+        if (!node)
+            return;
         if (shadowRoot.mode() != ShadowRootMode::Open)
             closedShadowDepth--;
         if (exitingShadowTreeOfTarget)