What sense makes medium_large_size_h => 0?

It appears that it’s eventually used as a parameter to wp_constrain_dimensions where ‘0’ means ‘no limit’.

It’s only used directly in media.php:85

  } elseif ( 'medium_large' === $size ) {
    $max_width  = intval( get_option( 'medium_large_size_w' ) );
    $max_height = intval( get_option( 'medium_large_size_h' ) );

    if ( intval( $content_width ) > 0 ) {
      $max_width = min( intval( $content_width ), $max_width );
    }

$max_height then used at :135

return wp_constrain_dimensions( $width, $height, $max_width, $max_height );

Docs here show 0 means no limit