fix: add null check for m_defSinkInter in sound applet

Added null pointer check for m_defSinkInter before accessing its
properties in removeDisabledDevice method. This prevents potential
segmentation faults when the default sink interface is not properly
initialized or has been destroyed.

Influence:
1. Test removing disabled audio devices when m_defSinkInter is null
2. Verify sound applet stability during device hot-plug operations
3. Test audio device switching scenarios with multiple sound cards
4. Verify no crashes occur when disabling audio devices

fix: 在声音小程序中添加对 m_defSinkInter 的空指针检查

在 removeDisabledDevice 方法中访问 m_defSinkInter 属性前添加了空指针检
查。这可以防止当默认接收器接口未正确初始化或已被销毁时可能发生的段错误。

Influence:
1. 测试当 m_defSinkInter 为空时移除禁用的音频设备
2. 验证在设备热插拔操作期间声音小程序的稳定性
3. 测试多声卡场景下的音频设备切换
4. 验证禁用音频设备时不会发生崩溃

PMS: BUG-347845

Author: mhduiy

plugins/dde-dock/sound/soundapplet.cpp

@@ -319,7 +319,7 @@ void SoundApplet::enableDevice(bool flag)
 void SoundApplet::removeDisabledDevice(QString portName, unsigned int cardId)
 {
     removePort(SoundCardPort::compositeKey(cardId, portName));
-    if (m_defSinkInter->activePort().name == portName && m_defSinkInter->card() == cardId) {
+    if (m_defSinkInter && m_defSinkInter->activePort().name == portName && m_defSinkInter->card() == cardId) {
         enableDevice(false);
     }
 }