obs-nvenc: Fix GPU selector visibility on dual-GPU systems

[0x1stvan]

Description

This change ensures the GPU (encoder device) selector is visible whenever at least one compatible device is detected, rather than requiring two or more devices.

Motivation and Context

Problem: On systems where a previously saved GPU encoder device has been removed or disabled, OBS returns a CUDA_ERROR_INVALID_DEVICE error when attempting to stream or record. In dual-GPU configurations, the device selector dropdown not appear, leaving users unable to select the remaining valid GPU through the UI.

How Has This Been Tested?

Not a breaking change, but tested the build on a dual-GPU setup with Windows 11 Professional (x64) Build 26100.7171 (24H2)

Types of changes

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.