Issues #2522: Only a section of items being returned in a directory.

[ArthurMousatov]

Description

This is a quick fix for issue #2522. From what I've seen, the issue seems to happen at Listing.vue:colunmsResize:614:

1. As the css() call may return null, items becomes null and as a result, causes an exception.
2. This exceptions stops the creation of the window listeners in the mounted() function.
3. Since there is no scroll event expanding the items on the page, only the initial amount of items is shown.

A quick return on items being null seems to fix the issue.

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Further comments