fix: Open filter window always in top

[4513ECHO]

SSIA

Before this PR, you have seen following window layout when doing below steps:

• Set uiParams.split to horizontal
• Set uiParams.previewSplit to vertical
• call openFilterWindow action after preview or togglePreview action:

┌───────────────┬─────────────┐
│ ddu-ff-filter │             │
├───────────────┤             │
│               │             │
│               │   preview   │
│     ddu-ff    │             │
│               │             │
│               │             │
└───────────────┴─────────────┘

After this PR:

┌─────────────────────────────┐
│        ddu-ff-filter        │
├───────────────┬─────────────┤
│               │             │
│               │             │
│     ddu-ff    │   preview   │
│               │             │
│               │             │
└───────────────┴─────────────┘