[Autofill Assistant] Fixes missing return.

When details are empty and no UI update is needed we should return.

Bug: 806868
Change-Id: Ibc644b11f135d9fab082b942f8939257b9933b1e
Reviewed-on: https://chromium-review.googlesource.com/c/1345078Reviewed-by: Stephane Zermatten <szermatt@chromium.org>
Commit-Queue: Lukasz Suder <lsuder@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610004}

chrome/android/java/src/org/chromium/chrome/browser/autofill_assistant/AutofillAssistantUiController.java

@@ -283,6 +283,7 @@ public class AutofillAssistantUiController implements AutofillAssistantUiDelegat
         if (mCurrentDetails.isEmpty() && newDetails.isEmpty()) {
             // No update on UI needed.
             nativeOnShowDetails(mUiControllerAndroid, /* canContinue= */ true);
+            return;
         }
 
         Details mergedDetails = Details.merge(mCurrentDetails, newDetails);