Check for existence of key material on store/load

Signed-off-by: Steven Cooreman <steven.cooreman@silabs.com>
diff --git a/library/psa_crypto_storage.c b/library/psa_crypto_storage.c
index 1ebd20e..10a1ad3 100644
--- a/library/psa_crypto_storage.c
+++ b/library/psa_crypto_storage.c
@@ -374,8 +374,12 @@
     uint8_t *storage_data;
     psa_status_t status;
 
+    /* All keys saved to persistent storage always have a key context */
+    if( data == NULL || data_length == 0 )
+        return( PSA_ERROR_INVALID_ARGUMENT );
+
     if( data_length > PSA_CRYPTO_MAX_STORAGE_SIZE )
-        return PSA_ERROR_INSUFFICIENT_STORAGE;
+        return( PSA_ERROR_INSUFFICIENT_STORAGE );
     storage_data_length = data_length + sizeof( psa_persistent_key_storage_format );
 
     storage_data = mbedtls_calloc( 1, storage_data_length );
@@ -426,6 +430,11 @@
     status = psa_parse_key_data_from_storage( loaded_data, storage_data_length,
                                               data, data_length, attr );
 
+    /* All keys saved to persistent storage always have a key context */
+    if( status == PSA_SUCCESS &&
+        ( *data == NULL || *data_length == 0 ) )
+        status = PSA_ERROR_STORAGE_FAILURE;
+
 exit:
     mbedtls_free( loaded_data );
     return( status );