Fixed feature Enabled Event Pending Cache

[Limraj]

To Reproduce

1. Login as admin;
2. Go to 'System Settings', checked 'Enabled Event Pending Cache' and save 'Other settings';
3. Create Virtual Data Source as vds_1(enabled, update 5s) and Virtual Data Point as vdp_1 (settable, enabled, numeric)
4. For vdp_1 added Event Detector type Change with Information level;
5. Added Watch Lists as wl_1 with point 'vds_1 - vdp_1';
6. Change value on vds_1 - vdp_1 then generate Event;
7. After 2 min Go to 'Alarms' then no visible generated new Event -> error;

Spec:

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Scada-LTS Version: >=2.7.7;