Use blog info as alternate, so upon activation of theme, you will see blog name instead of broken image
<?php if(!empty($redux_ti['logo']['url'])) : ?>
<a class="navbar-brand" href="<?php echo esc_url( home_url( '/' ) ); ?>">
<img src="<?php echo esc_url($redux_ti['logo']['url']); ?>" alt="<?php bloginfo('name'); ?>" class="logo">
</a>
<?php else : ?>
<a class="navbar-brand sitename" href="<?php echo esc_url( home_url( '/' ) ); ?>" rel="home">
<?php bloginfo( 'name' ); ?>
</a>
<?php endif; ?>