[29.x] SOA: Clear previous search filter

[VolodySyn]

Fixes AB#649167

Summary
Clears the stale SystemId filter before processing a new item search. This prevents previous search results from restricting subsequent searches and ensures empty searches correctly reset the search state.

[alexei-dobriansky]

Good Sense Reviewer - Round 1

Recommendation: Accept

What this PR does

This change clears the SystemId filter on the Item record before a new Sales Order Agent item search is processed. That removes stale record narrowing from the previous search while keeping the existing early exit for repeated filters and empty searches. The code then rebuilds the item candidate filter from the current search text, so the new search is not limited by the prior selected item.

Problem-solution fit

Fit: Strong

The reported problem is that a successful item search can leave a SystemId filter behind and affect the next search. The one-line change targets that leftover filter before the new item filter is built, which matches the described failure mode.

Suggestions

No suggestions.

Risk assessment and necessity

Risk: The regression surface is the Sales Order Agent item lookup and multi-item availability search. The change only removes a stale SystemId filter after the search text has changed, so it should not affect normal item filtering, availability filtering, or variant resolution.

Necessity: The change is needed because a stale record filter can make later searches look empty or too narrow even when matching items exist. The scope is small and limited to clearing that stale search state.

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