Stop crashing in Low Power cluster Sleep command if there's no delegate.

We were forgetting to return after sending the error response, so
ended up dereferencing the null delegate.

Fixes project-chip#19481

src/app/clusters/low-power-server/low-power-server.cpp

@@ -29,6 +29,7 @@
 #include <app/ConcreteCommandPath.h>
 #include <app/util/af.h>
 #include <platform/CHIPDeviceConfig.h>
+#include <protocols/interaction_model/StatusCode.h>
 
 using namespace chip;
 using namespace chip::app::Clusters::LowPower;
@@ -87,22 +88,23 @@ void SetDefaultDelegate(EndpointId endpoint, Delegate * delegate)
 bool emberAfLowPowerClusterSleepCallback(app::CommandHandler * command, const app::ConcreteCommandPath & commandPath,
                                          const Commands::Sleep::DecodableType & commandData)
 {
-    CHIP_ERROR err      = CHIP_NO_ERROR;
+    using Protocols::InteractionModel::Status;
+
     EndpointId endpoint = commandPath.mEndpointId;
 
     Delegate * delegate = GetDelegate(endpoint);
-    VerifyOrExit(isDelegateNull(delegate, endpoint) != true, err = CHIP_ERROR_INCORRECT_STATE);
-
-exit:
-    if (err != CHIP_NO_ERROR)
+    Status status;
+    if (isDelegateNull(delegate, endpoint))
     {
-        ChipLogError(Zcl, "emberAfLowPowerClusterSleepCallback error: %s", err.AsString());
-        emberAfSendImmediateDefaultResponse(EMBER_ZCL_STATUS_FAILURE);
+        ChipLogError(Zcl, "emberAfLowPowerClusterSleepCallback: no delegate");
+        status = Status::Failure;
     }
-
-    bool success         = delegate->HandleSleep();
-    EmberAfStatus status = success ? EMBER_ZCL_STATUS_SUCCESS : EMBER_ZCL_STATUS_FAILURE;
-    emberAfSendImmediateDefaultResponse(status);
+    else
+    {
+        bool success = delegate->HandleSleep();
+        status       = success ? Status::Success : Status::Failure;
+    }
+    command->AddStatus(commandPath, status);
     return true;
 }