src: fix logically dead code reported by Coverity

Value of the `nwrite` variable will always be less than 0 when it
reaches the `switch` statement because of the previous check, which
causes `case 0` to never be executed, change the check to allow 0 or
less.

PR-URL: #48589
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>

src/quic/session.cc

@@ -792,7 +792,7 @@ uint64_t Session::SendDatagram(Store&& data) {
                                                  1,
                                                  uv_hrtime());
 
-    if (nwrite < 0) {
+    if (nwrite < 1) {
       // Nothing was written to the packet.
       switch (nwrite) {
         case 0: {