LibWeb: Add some extra browsing context null checks

I saw a suspicious null dereference in
check_if_access_between_two_browsing_contexts_should_be_reported(),
but I have no idea how to reproduce it.

Still, it seems harmless to paper over it with a FIXME debug log.

Userland/Libraries/LibWeb/HTML/CrossOrigin/Reporting.cpp

@@ -35,12 +35,20 @@ void check_if_access_between_two_browsing_contexts_should_be_reported(
     auto accessor_accessed_relationship = AccessorAccessedRelationship::None;
 
     // 5. If accessed's top-level browsing context's opener browsing context is accessor or an ancestor of accessor, then set accessorAccessedRelationship to accessor is opener.
-    if (auto opener = accessed->top_level_browsing_context()->opener_browsing_context(); opener && (opener == &accessor || opener->is_ancestor_of(accessor)))
-        accessor_accessed_relationship = AccessorAccessedRelationship::AccessorIsOpener;
+    if (auto accessed_top_level_browsing_context = accessed->top_level_browsing_context()) {
+        if (auto opener = accessed_top_level_browsing_context->opener_browsing_context(); opener && (opener == &accessor || opener->is_ancestor_of(accessor)))
+            accessor_accessed_relationship = AccessorAccessedRelationship::AccessorIsOpener;
+    } else {
+        dbgln("FIXME: accessed's top-level browsing context is null in check_if_access_between_two_browsing_contexts_should_be_reported()");
+    }
 
     // 6. If accessor's top-level browsing context's opener browsing context is accessed or an ancestor of accessed, then set accessorAccessedRelationship to accessor is openee.
-    if (auto opener = accessor.top_level_browsing_context()->opener_browsing_context(); opener && (opener == accessed || opener->is_ancestor_of(*accessed)))
-        accessor_accessed_relationship = AccessorAccessedRelationship::AccessorIsOpenee;
+    if (auto accessor_top_level_browsing_context = accessor.top_level_browsing_context()) {
+        if (auto opener = accessor_top_level_browsing_context->opener_browsing_context(); opener && (opener == accessed || opener->is_ancestor_of(*accessed)))
+            accessor_accessed_relationship = AccessorAccessedRelationship::AccessorIsOpenee;
+    } else {
+        dbgln("FIXME: accessor's top-level browsing context is null in check_if_access_between_two_browsing_contexts_should_be_reported()");
+    }
 
     // FIXME: 7. Queue violation reports for accesses, given accessorAccessedRelationship, accessor's top-level browsing context's active document's cross-origin opener policy, accessed's top-level browsing context's active document's cross-origin opener policy, accessor's active document's URL, accessed's active document's URL, accessor's top-level browsing context's initial URL, accessed's top-level browsing context's initial URL, accessor's active document's origin, accessed's active document's origin, accessor's top-level browsing context's opener origin at creation, accessed's top-level browsing context's opener origin at creation, accessor's top-level browsing context's active document's referrer, accessed's top-level browsing context's active document's referrer, P, and environment.
     (void)accessor;