http: Discard output buffer on disconnect.

Prevents an assert.

ext/native/net/sinks.cpp

@@ -341,6 +341,12 @@ bool OutputSink::Flush(bool allowBlock) {
 	return true;
 }
 
+void OutputSink::Discard() {
+	read_ = 0;
+	write_ = 0;
+	valid_ = 0;
+}
+
 void OutputSink::Drain() {
 	// Avoid small reads if possible.
 	if (valid_ > PRESSURE) {

ext/native/net/sinks.h

@@ -51,6 +51,7 @@ public:
 	bool Printf(const char *fmt, ...);
 
 	bool Flush(bool allowBlock = true);
+	void Discard();
 
 	bool Empty();
 

ext/native/net/websocket_server.cpp

@@ -259,6 +259,8 @@ bool WebSocketServer::Process(float timeout) {
 			// Since select said it was readable, we assume this means disconnect.
 			closeReason_ = WebSocketClose::ABNORMAL;
 			open_ = false;
+			// Kill any remaining output too.
+			out_->Discard();
 			return false;
 		}