Add Null checks while processing pairing cancel intent

Use case: Exception while handling pairing cancel
          Intent received
1. Initiate pairing from DUT to remote
2. Power off DUT after getting pairing popup

Root Cause:Crash observed in settings application

Change-Id: Ia05fe196ecf6a1d4ec26f85b0cf984e23089c728
Fix: Fixed by adding Null check in PairingCancelHandler

packages/SettingsLib/src/com/android/settingslib/bluetooth/BluetoothEventManager.java

@@ -355,7 +355,9 @@ public final class BluetoothEventManager {
                 return;
             }
             int errorMsg = R.string.bluetooth_pairing_error_message;
-            Utils.showError(context, cachedDevice.getName(), errorMsg);
+            if (context != null && cachedDevice != null) {
+                Utils.showError(context, cachedDevice.getName(), errorMsg);
+            }
         }
     }