QmlJS: Fix lazy initialization of CppComponentValue::signalScopes.

Could lead to crashes when two threads initialize it at the same time.

Change-Id: Ia8e2c280c89087b1195451948c36a384e1098423
Reviewed-by: Leandro Melo <leandro.melo@nokia.com>

src/libs/qmljs/qmljsinterpreter.cpp

@@ -479,7 +479,7 @@ const ObjectValue *CppComponentValue::signalScope(const QString &signalName) con
             scopes->insert(generatedSlotName(method.methodName()), scope);
         }
         if (!_signalScopes.testAndSetOrdered(0, scopes)) {
-            delete _signalScopes;
+            delete scopes;
             scopes = _signalScopes;
         }
     }