vpx plugin has no features when built with Visual Studio 2019

$subject, this broke in the 1.16.1 binaries not sure how because 1.16.0 was built with VS 2017 and 1.16.1 with VS 2019. It's a regression from 1.16.0.

Before: size 1.8M, all features. After: size 32K, no features.

• Make the meson build file error out when the vpx plugin is enabled and no features were found gst-plugins-good!381 (merged)