fix: crashed on palette destroyed

[kegechen]

do not set value if control's window is null Issue: https://github.com/linuxdeepin/dtk/issues/193

[deepin-ci-robot]

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[deepin-bot[bot]]

TAG Bot

New tag: 5.6.34 DISTRIBUTION: unstable Suggest: synchronizing this PR through rebase #382

[deepin-bot[bot]]

Doc Check bot :green_circle: Document Coverage Check Passed!

[deepin-ci-robot]

deepin pr auto review

关键摘要:

• 在DQMLGlobalObjectPrivate构造函数中，使用lambda表达式连接qApp的aboutToQuit信号到全局变量g_appAboutToQuit，但没有处理可能出现的槽函数未连接的错误情况。
• DQuickControlColorSelector::updatePropertyFromName函数中，增加了对DQMLGlobalObjectPrivate::g_appAboutToQuit的检查，但没有更新注释来反映这一变化。

是否建议立即修改:

• 是

[deepin-bot[bot]]

TAG Bot

New tag: 5.0.35 DISTRIBUTION: unstable Suggest: synchronizing this PR through rebase #400

[deepin-bot[bot]]

TAG Bot

New tag: 5.7.1 DISTRIBUTION: unstable Suggest: synchronizing this PR through rebase #401