fix: showing/hiding empty conversation list placeholder - WPB-14386

[github-actions]

WPB-14386 [iOS] Empty screen placeholder hides conversations

This PR was automatically cherry-picked based on the following PR:

• fix: showing/hiding empty conversation list placeholder - WPB-14386 #2179

Original PR description:

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Issue

In some cases the empty screen placeholder doesn't get shown or hidden, see the ticket description.

Testing

on iPhone & iPad:

• Try to archive and unarchive the only conversation in the conversation list. Previously the empty screen placeholder wasn't added or removed.
• When the conversation list is empty, start a new conversation using the plus button in the navigation bar.

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Checklist

• Title contains a reference JIRA issue number like [WPB-XXX].
• Description is filled and free of optional paragraphs.
• Adds/updates automated tests.

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UI accessibility checklist

If your PR includes UI changes, please utilize this checklist:

• Make sure you use the API for UI elements that support large fonts.
• All colors are taken from WireDesign.ColorTheme or constructed using WireDesign.BaseColorPalette.
• New UI elements have Accessibility strings for VoiceOver.

[github-actions]

Test Results

    2 files    288 suites   2m 40s ⏱️
1 782 tests 1 782 ✅ 0 💤 0 ❌
1 790 runs  1 790 ✅ 0 💤 0 ❌

Results for commit a819cfb.

♻️ This comment has been updated with latest results.