QmlJS checks: Disable some checks when imports failed.

The important error in this case is on the import.

Change-Id: I3a547ca7ac44a89aba6819ea80ec52185071408a
Reviewed-on: http://codereview.qt-project.org/5879
Reviewed-by: Christian Kamm <christian.d.kamm@nokia.com>
Sanity-Review: Christian Kamm <christian.d.kamm@nokia.com>

src/libs/qmljs/qmljscheck.h

@@ -129,6 +129,8 @@ private:
     QList<AST::Node *> _chain;
     QStack<StringSet> m_idStack;
     QStack<StringSet> m_propertyStack;
+
+    bool _importsOk;
 };
 
 } // namespace QmlJS