fall back to default panel agent when not having a location specific default agent (microsoft#210070)

Author: jrieken

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

@@ -338,14 +338,14 @@ export class ChatService extends Disposable implements IChatService {
 			model.startInitialize();
 
 			await this.extensionService.whenInstalledExtensionsRegistered();
-			const defaultAgentData = this.chatAgentService.getContributedDefaultAgent(model.initialLocation);
+			const defaultAgentData = this.chatAgentService.getContributedDefaultAgent(model.initialLocation) ?? this.chatAgentService.getContributedDefaultAgent(ChatAgentLocation.Panel);
 			if (!defaultAgentData) {
 				throw new ErrorNoTelemetry('No default agent contributed');
 			}
 
 			await this.extensionService.activateByEvent(`onChatParticipant:${defaultAgentData.id}`);
 
-			const defaultAgent = this.chatAgentService.getDefaultAgent(model.initialLocation);
+			const defaultAgent = this.chatAgentService.getActivatedAgents().find(agent => agent.id === defaultAgentData.id);
 			if (!defaultAgent) {
 				// Should have been registered during activation above!
 				throw new ErrorNoTelemetry('No default agent registered');