Fall back to using the NULL audio backend if the default backends don't provide any devices.

[binary1248]

Title.

Because audio context creation will succeed even if the selected context cannot provide any devices, the NULL backend is never selected even on systems on which we know no audio device exists. We have to check for the existence of devices ourselves after creating a normal context and force miniaudio to create a NULL context if we determine a normal context would not provide us with any devices.

Should help with testing on audio device-less systems such as when running CI.

[coveralls]

Pull Request Test Coverage Report for Build 8886478280

Details

• 0 of 42 (0.0%) changed or added relevant lines in 2 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 51.46%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/SFML/Audio/AudioDevice.cpp	0	21	0.0%
src/SFML/Audio/SoundRecorder.cpp	0	21	0.0%

Files with Coverage Reduction	New Missed Lines	%
include/SFML/Audio/SoundRecorder.hpp	1	0.0%

Totals
Change from base Build 8884078579:	-0.1%
Covered Lines:	10437
Relevant Lines:	19137

---

💛 - Coveralls

[ChrisThrasher]

https://github.com/ChrisThrasher/SFML/actions/runs/8886742515

I rebased my tests onto this PR and we're still getting Linux and Windows CI failures. It did fix the macOS issues though.

[eXpl0it3r]

Seems to work fine