Project: Make sure id() will never change

Warn and ignore attempts to change the id() of a project.

Change-Id: I26c7c585e87d8be7b9fb8da3b3685b252e05f070
Reviewed-by: Eike Ziller <eike.ziller@qt.io>

src/plugins/projectexplorer/project.cpp

@@ -505,6 +505,7 @@ void Project::setDisplayName(const QString &name)
 
 void Project::setId(Core::Id id)
 {
+    QTC_ASSERT(!d->m_id.isValid(), return); // Id may not change ever!
     d->m_id = id;
 }