Potentially fix welcome banner in agent panel not going away (#37879)

Potentially fixes #37367. Just going ahead with the change even though
it's unclear whether this is the fix, since it is quite low risk.

Release Notes:

- N/A

crates/agent_ui/src/agent_panel.rs

@@ -3008,6 +3008,9 @@ impl AgentPanel {
             _ => {
                 let history_is_empty = if cx.has_flag::<GeminiAndNativeFeatureFlag>() {
                     self.acp_history_store.read(cx).is_empty(cx)
+                        && self
+                            .history_store
+                            .update(cx, |store, cx| store.recent_entries(1, cx).is_empty())
                 } else {
                     self.history_store
                         .update(cx, |store, cx| store.recent_entries(1, cx).is_empty())