net/http: fix nil didTimeout deref when a client dial fails

Client.do calls didTimeout() on the error path (line 461), and the contract is
that send() returns a non-nil didTimeout whenever err != nil. TinyGo dropped
setRequestCancel but left the roundTrip error path returning the nil named
return value, so any http.Client{Timeout: ...} request whose dial failed (e.g.
connection refused) panicked with a nil func-value dereference instead of
returning the error. Return alwaysFalse on those error paths, matching the
other error returns in send().

Verified: http.Client{Timeout}.Get to a refused port now returns
"connection refused" instead of panicking.

http/client.go

@@ -213,10 +213,14 @@ func send(req *Request, deadline time.Time) (resp *Response, didTimeout func() b
 
 		// TINYGO: Remove TLS error check
 
-		return nil, didTimeout, err
+		// didTimeout must be non-nil whenever err != nil: c.do calls
+		// didTimeout() on the error path. The named return is nil here (TinyGo
+		// dropped setRequestCancel), so return alwaysFalse instead to avoid a
+		// nil func-value dereference on a failed dial.
+		return nil, alwaysFalse, err
 	}
 	if resp == nil {
-		return nil, didTimeout, fmt.Errorf("http: sendit returned a nil *Response with a nil error")
+		return nil, alwaysFalse, fmt.Errorf("http: sendit returned a nil *Response with a nil error")
 	}
 
 	// TINYGO: Skip check for resp.Body == nil since we'll set it in roundTrip