fix(amplify_auth_cognito): throws signedout exception (#730)

Author: haverchuck

packages/amplify_auth_cognito/android/src/main/kotlin/com/amazonaws/amplify/amplify_auth_cognito/AuthCognito.kt

@@ -571,7 +571,15 @@ public class AuthCognito : FlutterPlugin, ActivityAware, MethodCallHandler, Plug
   }
 
   fun prepareCognitoSessionFailure(@NonNull flutterResult: Result, @NonNull result: AWSCognitoAuthSession) {
-    errorHandler.handleAuthError(flutterResult, AuthException.SessionExpiredException())
+    // If a User Pool token's error is a SignedOutException, we send SignedOutException as
+    // method call response because this indicates that the problem is not expired tokens,
+    // but total lack of authentication (i.e. the user is signed out)
+    var sessionException: AuthException = if (result.userPoolTokens.error is AuthException.SignedOutException) {
+      AuthException.SignedOutException()
+    } else {
+      AuthException.SessionExpiredException()
+    }
+    errorHandler.handleAuthError(flutterResult, sessionException)
   }
 
   fun prepareSessionResult(@NonNull flutterResult: Result, @NonNull result: AuthSession) {