Fix - Ensure selected states is always an array in inventory selector

[RomainLvr]

Checklist before requesting a review

Please delete options that are not relevant.

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• I have updated the CHANGELOG with a short functional description of the fix or new feature.
• This change requires a documentation update.

Description

• It fixes !44484
• Here is a brief description of what this PR does

When a user submits a search with an empty state field in mreporting reports (e.g. "Computers by OS"), the session stores an empty string instead of an array for the states selector. This causes a fatal error when count() is called on it, requiring a session cache flush to recover.

Added an is_array() guard after reading the session value so it always falls back to an empty array, preventing the crash.