ProjectWizard: Prevent crash on changes to VCS settings

The ProjectExtension kept a pointer to a page which is destroyed
once the wizard is done and accessed it whenever VCS settings
were touched.

Task-number: QTCREATORBUG-9412
Change-Id: Iabe33d877a3d614ab7470c5e11fe26f7de1bb69c
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>

src/plugins/projectexplorer/projectfilewizardextension.cpp

@@ -177,7 +177,7 @@ struct ProjectWizardContext
     QList<Core::IVersionControl*> versionControls;
     QList<Core::IVersionControl*> activeVersionControls;
     QList<ProjectEntry> projects;
-    ProjectWizardPage *page;
+    QPointer<ProjectWizardPage> page; // this is managed by the wizard!
     bool repositoryExists; // Is VCS 'add' sufficient, or should a repository be created?
     QString commonDirectory;
     const Core::IWizard *wizard;
@@ -195,7 +195,7 @@ void ProjectWizardContext::clear()
     activeVersionControls.clear();
     projects.clear();
     commonDirectory.clear();
-    page = 0;
+    page.clear();
     repositoryExists = false;
     wizard = 0;
 }
@@ -329,6 +329,9 @@ void ProjectFileWizardExtension::firstExtensionPageShown(
 
 void ProjectFileWizardExtension::initializeVersionControlChoices()
 {
+    if (m_context->page.isNull())
+        return;
+
     // Figure out version control situation:
     // 1) Directory is managed and VCS supports "Add" -> List it
     // 2) Directory is managed and VCS does not support "Add" -> None available