fix(taskManager):修复desktop文件中Icon路径不存在时图标处理错误的问题

QIcon在添加了不存在的文件时，isNull会返回false

widgets/ukui-task-manager/task-manager-item.cpp

@@ -253,7 +253,15 @@ void TaskManagerItem::init()
 
     d->m_quickWidget = WidgetInfo::self()->widgetFor(d->m_ID);
     d->m_name = d->m_xdf.localizedValue("Name").toString();
-    d->m_icon = QIcon::fromTheme(d->m_xdf.iconName());
+
+    QString iconName = d->m_xdf.iconName();
+    if(iconName.startsWith("/")) {
+        if(QFile::exists(iconName)) {
+            d->m_icon = QIcon(iconName);
+        }
+    } else {
+        d->m_icon = QIcon::fromTheme(iconName);
+    }
 
     if(!winIDs().isEmpty()) {
         //TODO： 获取groupLeader窗口的图标？