If starting a transaction fails, wipe the transaction data

Nothing has been saved to disk yet, but there is stale data in
psa_crypto_transaction. This stale data should not be reused, but do
wipe it to reduce the risk of it mattering somehow in the future.
diff --git a/library/psa_crypto.c b/library/psa_crypto.c
index 92c9668..b2fc26e 100644
--- a/library/psa_crypto.c
+++ b/library/psa_crypto.c
@@ -993,6 +993,7 @@
         status = psa_crypto_save_transaction( );
         if( status != PSA_SUCCESS )
         {
+            (void) psa_crypto_stop_transaction( );
             /* TOnogrepDO: destroy what can be destroyed anyway */
             return( status );
         }
@@ -1484,7 +1485,10 @@
         psa_crypto_transaction.key.id = slot->persistent_storage_id;
         status = psa_crypto_save_transaction( );
         if( status != PSA_SUCCESS )
+        {
+            (void) psa_crypto_stop_transaction( );
             return( status );
+        }
     }
 #endif /* MBEDTLS_PSA_CRYPTO_SE_C */