Fix slash comands in /help that don't have sample queries (#227027)

Fix microsoft/vscode-copilot#7742

src/vs/workbench/contrib/chat/common/chatServiceImpl.ts

@@ -481,9 +481,8 @@ export class ChatService extends Disposable implements IChatService {
 	}
 
 	async sendRequest(sessionId: string, request: string, options?: IChatSendRequestOptions): Promise<IChatSendRequestData | undefined> {
-
 		this.trace('sendRequest', `sessionId: ${sessionId}, message: ${request.substring(0, 20)}${request.length > 20 ? '[...]' : ''}}`);
-		if (!request.trim()) {
+		if (!request.trim() && !options?.slashCommand && !options?.agentId) {
 			this.trace('sendRequest', 'Rejected empty message');
 			return;
 		}