[main] bug 642230 - Enhance FA General Report logic and add tests for Tax Deprec. Group and FA Posting Group handling

[DavidHolusa]

What & why

The SetFAPostingGroup procedure in codeunit "FA General Report" (and the analogous SetFATaxDeprGroup in CZ localization codeunit "FA General Report CZF") could overwrite the "FA Posting Group" (or "Tax Deprec. Group Code CZF") on the Fixed Asset card with a blank value. This happened when the related FA Depreciation Book record had an empty posting group — the code only checked whether the values differed, without verifying that the source value was non-blank. As a result, running reports like "Fixed Asset - G/L Analysis" with Group Totals set to "FA Posting Group" (or "Tax Depreciation Group") would silently clear the field on the FA card.

The fix adds a guard condition (FADeprBook."FA Posting Group" <> '') (and (FADepreciationBook."Tax Deprec. Group Code CZF" <> '') for CZ) so that the field is only updated when the depreciation book carries a meaningful value. Direct unit tests for both SetFAPostingGroup and SetFATaxDeprGroup are added to cover the regression.

Linked work

Fixes AB#643230

How I validated this

• I read the full diff and it contains only changes I intended.
• I built the affected app(s) locally with no new analyzer warnings.
• I ran the change in Business Central and confirmed it behaves as expected.
• I added or updated tests for the new behavior, or explained below why none are needed.

What I tested and the outcome

• Created a Fixed Asset with FA Posting Group "EQUIPMENT", then created an FA Depreciation Book with blank FA Posting Group. Before the fix, running "Fixed Asset - G/L Analysis" cleared the FA Posting Group on the card. After the fix, the value remains "EQUIPMENT".
• Created a Fixed Asset with FA Posting Group "EQUIPMENT", then set a different non-blank FA Posting Group "VEHICLES" on the FA Depreciation Book. After running the report, the FA card correctly updated to "VEHICLES".
• Same scenarios validated for CZ localization with Tax Deprec. Group Code CZF field.
• Added 2 new direct unit tests in W1 (SetFAPostingGroupDoesNotClearFAPostingGroupWhenDepreciationBookPostingGroupIsBlank, SetFAPostingGroupUpdatesFAPostingGroupWhenDepreciationBookPostingGroupIsDifferentAndNotBlank) — both pass.
• Added 2 new direct unit tests in CZ (SetFATaxDeprGroupDoesNotClearTaxDepreciationGroupWhenDepreciationBookTaxDepGroupIsBlank, SetFATaxDeprGroupUpdatesTaxDepreciationGroupWhenDepreciationBookTaxDepGroupIsDifferentAndNotBlank) — both pass.

Risk & compatibility

None. The change is additive — it only prevents a destructive side effect (clearing a field). No breaking changes, no data migration needed, no new permissions required. The guard condition is consistent with the existing pattern where other "Set*" procedures in the same codeunit already validate before modifying.