Multi level hierarchies not displaying sub albums

After adding a 3rd level of albums I noticed that the gallery view was not displaying sub albums. This is because node_gallery_hierarchy_get_subgalleries() is not correctly searching children.

Specifically, its trying to keep track of children in an array and does the following

$children += $gallery->children;

According to http://php.net/manual/en/language.operators.array.php, "+=" is not a valid operator for arrays. That page claims that "+" is a valid operator but I verified that

$children = $children + $gallery->children;

does not work with php 5.4.7. What does work is
$children = array_merge($children, $gallery->children);

Patch included.