[10.x] Refactored chunk method using Null coalescing operator

[kitamatsu-rui]

I've simplified and improved the readability of the chunk method in Foundation/vite.php by incorporating the null coalescing operator.

[browner12]

Taylor rarely merges things like this. But be aware, it also technically changes behavior. Null coalesce does an isset and null check, where the previous code was only doing an isset check.