Fix gpulayers autodetection for cublas & clblast backends

[matoro]

This fixes --gpulayers -1 paired with either --usecublas or --useclblast with no additional arguments.

[YellowRoseCx]

What issue were you experiencing with this? Auto detect layers works fine for me on Linux and Windows

[matoro]

What issue were you experiencing with this? Auto detect layers works fine for me on Linux and Windows

If you use e.g. --usecublas --gpulayers -1, then args.usecublas = [], not None, so it errors with No GPU backend found, or could not automatically determine GPU layers. Please set it manually., even though a GPU is present. Same for useclblast. It works only if you pass an argument, e.g. --usecublas lowvram --gpulayers -1.

[YellowRoseCx]

Ahh okay. On the GUI, when selecting CuBLAS, it passes "normal" to the arguments list, but with the CLI it makes the list empty, and because
[] (empty list): returns Falsy
["normal"]: returns Truthy,

The code would work in GUI but not via CLI; checking if it's not None rather than truthiness of the argument would make it work in both situations.
Thanks for catching that!