tcp: actually send finish when needed by the state

fix #18327 after hrev57546

Change-Id: I352a325f3c2068d06996c278246f7a30f5bfcbe0
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7504
Reviewed-by: nephele nephele <nep-git@packageloss.eu>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

src/add-ons/kernel/network/protocols/tcp/TCPEndpoint.cpp

@@ -2213,7 +2213,7 @@ TCPEndpoint::_SendQueued(bool force)
 		sendWindow -= consumedWindow;
 
 	uint32 length = min_c(fSendQueue.Available(fSendNext), sendWindow);
-	if (length == 0) {
+	if (length == 0 && !state_needs_finish(fState)) {
 		// Nothing to send.
 		return B_OK;
 	}