Change the default value of initialized cipher operation to NONE

This way, an initialized cipher context but without a key set can be identified.
Signed-off-by: Andrzej Kurek <[email protected]>

library/cipher.c

@@ -186,6 +186,7 @@ int mbedtls_cipher_setup( mbedtls_cipher_context_t *ctx, const mbedtls_cipher_in
         return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
     mbedtls_platform_memset( ctx, 0, sizeof( mbedtls_cipher_context_t ) );
+    ctx->operation = MBEDTLS_OPERATION_NONE;
 
     if( NULL == ( ctx->cipher_ctx = cipher_info->base->ctx_alloc_func() ) )
         return( MBEDTLS_ERR_CIPHER_ALLOC_FAILED );