Fixed issue #1091: Bands disappear with explorer theme

[TetzkatLipHoka]

Fixes #1091.

Cause

With the explorer theme active, DetermineLineImageAndSelectLevel() suppresses the tree line under the expand button by overwriting the last line image entry with ltNone.

The band conversion in PaintTreeLines() however relies on its documented invariant that ltNone never appears as the last entry ("A no line entry can never appear as last entry so I don't need an end check here"): on ltNone it takes over the style of the entry to the right, which for the last entry is an out-of-bounds read of the dynamic array — with range checking enabled this raises ERangeError.

The resulting garbage styles made the bands of every collapsed node with children disappear, while expanded nodes stayed intact (they take the vsExpanded branch of the conversion) — matching the screenshot in the issue. Without a themed application manifest the bug does not reproduce, which is why it is easy to miss in test programs.

Fix

Skip the suppression when LineMode = lmBands: bands are box edges, not lines pointing at a button, so there is nothing to suppress. One condition, no behavior change for lmNormal.

Verification

• Reproduced with the reporter's project from the issue (themed manifest): before the fix the bands of all collapsed parent rows are missing; after the fix the rendering is identical to the unthemed one.
• New regression test Tests/VTBandsIssue1091Tests.pas renders offscreen and compares band pixels (count plus position checksum) with and without the tsUseExplorerTheme state, following the pattern of the existing paint tests. Without the fix it fails (53 of 1954 band pixels missing in the test scenario), with the fix it passes.
• Full test suite: no new failures (the two TestCopyHTML failures also occur on unmodified master).

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