Use standalone guard for undefined mode for consistency

Author: erikeldridge

packages/ai/src/methods/chrome-adapter.ts

@@ -68,7 +68,13 @@ export class ChromeAdapter {
    * separation of concerns.</p>
    */
   async isAvailable(request: GenerateContentRequest): Promise<boolean> {
-    if (!this.mode || this.mode === 'only_in_cloud') {
+    if (!this.mode) {
+      logger.debug(
+        `On-device inference unavailable because mode is undefined.`
+      );
+      return false;
+    }
+    if (this.mode === 'only_in_cloud') {
       logger.debug(
         `On-device inference unavailable because mode is "only_in_cloud".`
       );