[Freestyler] Remove last loading step on error

We may want to change the step to error instead,
but more often it's empty so we add no value for now.

Fixed: 369307147
Change-Id: I029d3dd9835b78de5f49b80a8763e36b6aa7def0
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/5904882
Reviewed-by: Ergün Erdoğmuş <ergunsh@chromium.org>
Commit-Queue: Nikolay Vitkov <nvitkov@chromium.org>

front_end/panels/freestyler/FreestylerPanel.ts

@@ -401,16 +401,18 @@ export class FreestylerPanel extends UI.Panel.Panel {
         }
 
         case ResponseType.ERROR: {
-          step.isLoading = false;
           systemMessage.error = data.error;
           systemMessage.suggestions = [];
           systemMessage.rpcId = undefined;
           this.#viewProps.isLoading = false;
-          if (data.error === ErrorType.ABORT) {
-            const lastStep = systemMessage.steps.at(-1);
+          const lastStep = systemMessage.steps.at(-1);
+          if (lastStep) {
             // Mark the last step as cancelled to make the UI feel better.
-            if (lastStep) {
+            if (data.error === ErrorType.ABORT) {
               lastStep.canceled = true;
+              // If error happens while the step is still loading remove it.
+            } else if (lastStep.isLoading) {
+              systemMessage.steps.pop();
             }
           }
         }