Work around os.cpus() returning an empty array on unsupported platforms

`os.cpus()` can return empty arrays on platforms not officially supported by Node.js. Use 1 as a minimum.

See <nodejs/node#38190>.

Co-authored-by: Mark Wubben <mark@novemberborn.net>

lib/api.js

@@ -246,14 +246,16 @@ export default class Api extends Emittery {
 				}
 			}));
 
-			// Resolve the correct concurrency value.
-			let concurrency = Math.min(os.cpus().length, isCi ? 2 : Number.POSITIVE_INFINITY);
-			if (apiOptions.concurrency > 0) {
-				concurrency = apiOptions.concurrency;
-			}
-
+			// Resolve the correct concurrency value. Note that `os.cpus()` can return empty arrays on
+			// platforms not officially supported by Node.js. Use 1 as a minimum.
+			// See <https://github.com/nodejs/node/issues/38190>.
+			let concurrency = Math.max(1, os.cpus().length);
 			if (apiOptions.serial) {
 				concurrency = 1;
+			} else if (apiOptions.concurrency > 0) {
+				concurrency = apiOptions.concurrency;
+			} else if (isCi) {
+				concurrency = 2;
 			}
 
 			const deregisteredSharedWorkers = [];