Describe the bug

For the PV-Battery loss diagram, the lossdiag.lk script adds bifacial gain to the diagram regardless of whether "module is bifacial" is enabled on the Module page. This makes it appear that non-bifacial modules experience bifacial gain. However, the "Nominal DC electricity (kWh)" value is correct, and does not include bifacial gain.

To Reproduce

Steps to reproduce the behavior:

1. Create a PV-Battery case with any financial model.
2. Verify that Module is bifacial on the Module page is not checked.
3. Run a simulation.
4. Go to Losses tab on Results page and see bifacial gain.

Expected behavior

Bifacial gain should only appear on loss diagram for bifacial modules for all Detailed PV and Detailed PV-battery configurations.

Note that pvsamv1 calculates and reports POA rear-side bifacial gain (annual_poa_rear_gain_percent) regardless of whether module is bifacial.