Fix boot crash in all-clusters-app on esp32

#10907 added some
identify bits on Linux only but changed the core cluster impl to
assume that those bits are always there.

This change stops assuming that identify is actually configured on
every endpoint that supports it, since nothing enforces that.

src/app/clusters/identify-server/identify-server.cpp

@@ -106,7 +106,11 @@ static inline void unreg(Identify * inst)
 
 void emberAfIdentifyClusterServerInitCallback(EndpointId endpoint)
 {
-    (void) Clusters::Identify::Attributes::IdentifyType::Set(endpoint, inst(endpoint)->mIdentifyType);
+    Identify * identify = inst(endpoint);
+    if (identify != nullptr)
+    {
+        (void) Clusters::Identify::Attributes::IdentifyType::Set(endpoint, identify->mIdentifyType);
+    }
 }
 
 static void onIdentifyClusterTick(chip::System::Layer * systemLayer, void * appState)