fix: retry immediately on non-positive numeric Retry-After header

The numeric Retry-After branch multiplied the header value by 1000 without
guarding non-positive results, so `Retry-After: 0` produced a falsy delay
that fell through to exponential backoff instead of retrying immediately.
The RFC-1123 date branch already clamps non-positive values to 1ms; mirror
that guard in the numeric branch so a non-positive Retry-After retries at
once.

source/core/index.ts

@@ -532,6 +532,10 @@ export default class Request extends Duplex implements RequestEvents<Request> {
 							}
 						} else {
 							retryAfter *= 1000;
+
+							if (retryAfter <= 0) {
+								retryAfter = 1;
+							}
 						}
 					}