Fix compatibility with native Fetch being disabled on Node.js (#494)

Author: sxzz

source/core/constants.ts

@@ -5,8 +5,9 @@ export const supportsRequestStreams = (() => {
 	let duplexAccessed = false;
 	let hasContentType = false;
 	const supportsReadableStream = typeof globalThis.ReadableStream === 'function';
+	const supportsRequest = typeof globalThis.Request === 'function';
 
-	if (supportsReadableStream) {
+	if (supportsReadableStream && supportsRequest) {
 		hasContentType = new globalThis.Request('https://a.com', {
 			body: new globalThis.ReadableStream(),
 			method: 'POST',