meson: Fix Windows CUDA dependency check

Python returns 'None' string for unknown environment
3 jobs for fix-meson-build in 4 minutes and 16 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Preparation
passed manifest #49556

00:00:20

 
  Build
passed build fedora x86_64 #49557

00:01:41

 
  Full Builds
passed build android arm64 api28 #49558

00:02:15