Fix: HttpHandler is calling HttpResponse::Finish twice for 404s

fixes #10024

lib/remote/httphandler.cpp

@@ -104,7 +104,6 @@ void HttpHandler::ProcessRequest(const ApiUser::Ptr& user, HttpRequest& request,
 		response.AddHeader("Content-Type", "text/html");
 		String msg = "<h1>Not found</h1>";
 		response.WriteBody(msg.CStr(), msg.GetLength());
-		response.Finish();
 		return;
 	}
 }

lib/remote/httpresponse.cpp

@@ -72,6 +72,9 @@ void HttpResponse::WriteBody(const char *data, size_t count)
 {
 	ASSERT(m_State == HttpResponseHeaders || m_State == HttpResponseBody);
 
+	if (count == 0)
+		return;
+
 	if (m_Request.ProtocolVersion == HttpVersion10) {
 		if (!m_Body)
 			m_Body = new FIFO();
@@ -86,6 +89,9 @@ void HttpResponse::WriteBody(const char *data, size_t count)
 
 void HttpResponse::Finish(void)
 {
+	ASSERT(m_State != HttpResponseEnd);
+	m_State = HttpResponseEnd;
+
 	if (m_Request.ProtocolVersion == HttpVersion10) {
 		if (m_Body)
 			AddHeader("Content-Length", Convert::ToString(m_Body->GetAvailableBytes()));

lib/remote/httpresponse.hpp

@@ -31,7 +31,8 @@ enum HttpResponseState
 {
 	HttpResponseStart,
 	HttpResponseHeaders,
-	HttpResponseBody
+	HttpResponseBody,
+	HttpResponseEnd
 };
 
 /**