Projects: Fix misc settings widgets if vanished targets are shown

When vanished targets where shown in Projects, clicking on the project
specific settings showed a blank page.

There were hardcoded indices for the target and the misc settings. Get
the right child for the index directly instead.

Change-Id: I725d470ad04f8a227c91938efada76a757a7442c
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/projectexplorer/projectwindow.cpp

@@ -527,11 +527,11 @@ public:
         }
 
         case PanelWidgetRole:
-        case ActiveItemRole:
-            if (m_currentChildIndex == 0)
-                return m_targetsItem->data(column, role);
-            if (m_currentChildIndex == 1)
-                return m_miscItem->data(column, role);
+        case ActiveItemRole: {
+            TreeItem *child = childAt(m_currentChildIndex);
+            if (child)
+                return child->data(column, role);
+        }
         }
         return {};
     }