Cleanup dangling CommissioneedeviceProxy object on CASE session (#15902)

establishment failure

This cleans up the dangling CommissioneeDeviceProxy object that is
usually cleaned up in case of successful commissioning in
OnDeviceConnectedFn (i.e successful CASE session establishment upon
completion of commissioning).

Consequently, failure to establish CASE should do the same *if and only
if* the device that we failed to establish CASE with matches the device
being commissioned.

Tests:
- Ensured we hit a VerifyOrDie error due to an open EC if CASE failed to
  establish, and then ensured that didn't manifest again with these
  changes.

src/controller/CHIPDeviceController.cpp

@@ -1501,12 +1501,23 @@ void DeviceCommissioner::OnDeviceConnectionFailureFn(void * context, PeerId peer
 {
     // CASE session establishment failed.
     DeviceCommissioner * commissioner = static_cast<DeviceCommissioner *>(context);
+
     ChipLogProgress(Controller, "Device connection failed. Error %s", ErrorStr(error));
     VerifyOrReturn(commissioner != nullptr,
                    ChipLogProgress(Controller, "Device connection failure callback with null context. Ignoring"));
     VerifyOrReturn(commissioner->mPairingDelegate != nullptr,
                    ChipLogProgress(Controller, "Device connection failure callback with null pairing delegate. Ignoring"));
 
+    //
+    // If a device is being commissioned currently and it is the very same device that we just failed to establish CASE with,
+    // we need to clean it up to prevent a dangling CommissioneeDeviceProxy object.
+    //
+    if (commissioner->mDeviceBeingCommissioned != nullptr && commissioner->mDeviceBeingCommissioned->GetPeerId() == peerId)
+    {
+        commissioner->ReleaseCommissioneeDevice(commissioner->mDeviceBeingCommissioned);
+        commissioner->mDeviceBeingCommissioned = nullptr;
+    }
+
     commissioner->mCASESessionManager->ReleaseSession(peerId);
     if (commissioner->mCommissioningStage == CommissioningStage::kFindOperational &&
         commissioner->mCommissioningDelegate != nullptr)