[AiAssistance] Fix changing panels breaking conversation when loading

I think, while doing refactoring, we updated the logic to save the
initial message to history after receiving the response from AidaClient.

This made `isEmpty` to return `false` when there is a loading request in
flight. So, whenever the user changed the panel while a request is in
flight; it changed the `#currentAgent`.

This CL fixes it by adding `isLoading` check to the
`#selectDefaultAgentIfNeeded` method.

Fixed: 395886018
Change-Id: Iedc50c968eec7bec9faa72f9dba3c9af84b38e2d
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/6253022
Auto-Submit: Ergün Erdoğmuş <[email protected]>
Reviewed-by: Alex Rudenko <[email protected]>
Commit-Queue: Ergün Erdoğmuş <[email protected]>
Commit-Queue: Alex Rudenko <[email protected]>

Author: ergunsh

front_end/panels/ai_assistance/AiAssistancePanel.ts

@@ -400,9 +400,10 @@ export class AiAssistancePanel extends UI.Panel.Panel {
   // We select the default agent based on the open panels if
   // there isn't any active conversation.
   #selectDefaultAgentIfNeeded(): void {
-    // If there already is an agent and not it is not empty,
-    // we don't automatically change the agent.
-    if (this.#currentAgent && !this.#currentAgent.isEmpty) {
+    // If there already is an agent and if it is not empty,
+    // we don't automatically change the agent. In addition to this,
+    // we don't change the current agent when there is a message in flight.
+    if ((this.#currentAgent && !this.#currentAgent.isEmpty) || this.#viewProps.isLoading) {
       return;
     }