Fix crash on Linux caused by null deref

(caused by 423d45cb)

BUG=481754

Review URL: https://codereview.chromium.org/1108173003

Cr-Commit-Position: refs/heads/master@{#327228}

chrome/browser/ui/views/autofill/card_unmask_prompt_views.cc

@@ -109,7 +109,8 @@ void CardUnmaskPromptViews::GotVerificationResult(
     // TODO(estade): it's somewhat jarring when the error comes back too
     // quickly.
     overlay_animation_.Reset();
-    storage_row_->SetAlpha(255);
+    if (storage_row_)
+      storage_row_->SetAlpha(255);
     progress_overlay_->SetVisible(false);
 
     if (allow_retry) {