unix: fix EINTR check in TestPselect

err == EINTR needs to be checked before err != nil for the interrupted
syscall to be retried properly.

Follow-up for CL 207284

Updates golang/go#35555

Change-Id: I76d569058b7985ec51f07909d86807a8b4911772
Reviewed-on: https://go-review.googlesource.com/c/sys/+/207292
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
diff --git a/unix/syscall_linux_test.go b/unix/syscall_linux_test.go
index 99a0f65..01a1028 100644
--- a/unix/syscall_linux_test.go
+++ b/unix/syscall_linux_test.go
@@ -289,11 +289,11 @@
 func TestPselect(t *testing.T) {
 	for {
 		_, err := unix.Pselect(0, nil, nil, nil, &unix.Timespec{Sec: 0, Nsec: 0}, nil)
-		if err != nil {
-			t.Fatalf("Pselect: %v", err)
-		} else if err == unix.EINTR {
+		if err == unix.EINTR {
 			t.Logf("Pselect interrupted")
 			continue
+		} else if err != nil {
+			t.Fatalf("Pselect: %v", err)
 		}
 		break
 	}