fix: Crash before starting on OpenBSD

core_affinity doesn't return any cores on OpenBSD, so we try to
clamp(1, 0). This is Less Good than fixing that crate, but at
least allows the server to start up.

src/service/sending/mod.rs

@@ -385,11 +385,13 @@ fn num_senders(args: &crate::Args<'_>) -> usize {
 	const MIN_SENDERS: usize = 1;
 	// Limit the number of senders to the number of workers threads or number of
 	// cores, conservatively.
-	let max_senders = args
-		.server
-		.metrics
-		.num_workers()
-		.min(available_parallelism());
+	let mut max_senders = args.server.metrics.num_workers();
+
+	// Work around some platforms not returning the number of cores.
+	let num_cores = available_parallelism();
+	if num_cores > 0 {
+		max_senders = max_senders.min(num_cores);
+	}
 
 	// If the user doesn't override the default 0, this is intended to then default
 	// to 1 for now as multiple senders is experimental.