Added a simple compilation test and linux CI (and fix linux build)

[Mrkol]

Trivial compilation test is required because the sample is windows-specific. Linux CI is needed because pull requests must stop breaking linux builds. The tiny m_Handle(VMA_NULL) -> m_Handle() fix is needed to fix linux CI.

As promised @adam-sawicki-a . Same day delivery because my CI is still broken =) (I will stop using master for my builds soon, I promise)