(#3729): when an exception is thrown during render, we no longer crash the compositor

[mattkae]

fixes #3729

What's new?

• The Renderer should be able to legitimately fail in some cases without causing a fatal error if the entire system.
• This does not necessarily solve the underlying problem, which is best recounted in this new issue: Output management on the gbm-kms platform is racy #3751

[AlanGriffiths]

I still have to think about whether this is the best way to handle the problem. It isn't entirely clear cut.

But, from a quick reading, we have a logging function to report exceptions and we should use it. (not just exception::what())

[AlanGriffiths]

Suggested change

	// An exception may be thrown by the underlying platform during render.
	// While bad, we do not want this to crash the compositor entirely.
	mir::log_error("Encountered exception while rendering: %s", e.what());
	// An exception may be thrown by the underlying platform during render.
	// While bad, we do not want this to crash the compositor entirely.
	log(logging::Severity::error, MIR_LOG_COMPONENT, std::current_exception(), "Encountered exception while rendering");

[mattkae]

I still have to think about whether this is the best way to handle the problem. It isn't entirely clear cut.

But, from a quick reading, we have a logging function to report exceptions and we should use it. (not just exception::what())

I don't love it either, which is why I made the other ticket to address the main underlying problem. If we would rather tackle that than eating the exception, I think that would be fair. Although I wouldn't necessarily consider a failure to render on a single output to be "fatal" per se, which is why I think the answer might be both.