KitMatcher: Make sure matcher function is properly initialized

This fixes some crashes in the TargetSetupPage and other places.

Also remove isValid method again. It was introduced to fix the same
crash that this patch also addresses, but introduces a bit more
complexity than this approach.

Change-Id: Iee80a2baffb2854b6fad8931d23a1da6d218f919
Reviewed-by: hjk <hjk121@nokiamail.com>

src/plugins/projectexplorer/project.cpp

@@ -102,9 +102,7 @@ public:
 ProjectPrivate::ProjectPrivate() :
     m_activeTarget(0),
     m_editorConfiguration(new EditorConfiguration()),
-    m_accessor(0),
-    m_requiredKitMatcher([](const Kit*) { return true; }),
-    m_preferredKitMatcher([](const Kit*) { return true; })
+    m_accessor(0)
 { }
 
 ProjectPrivate::~ProjectPrivate()