ToolChainKitInformation: Make use of ToolChainManager::isLoaded()

Warn when trying to access values not yet initialized, and avoid
doing so. Also invalidate toolchains in kits properly.

Change-Id: I3a98a2ca89ce43d9982d37bdee451c5122c788b2
Reviewed-by: Daniel Teske <daniel.teske@digia.com>

src/plugins/android/androidplugin.h

@@ -43,7 +43,8 @@ public:
     AndroidPlugin();
 
     bool initialize(const QStringList &arguments, QString *errorMessage);
-    void extensionsInitialized();
+    void extensionsInitialized() { }
+
 private slots:
     void kitsRestored();
 };