[Payments] Card unmask controller: nullcheck the delegate

The |delegate_| might be gone when the unmask response comes (we have
seen crashes). Guard it.

Bug: None
Change-Id: I4d656c0379c76383b616d564cf2d1dc024cffaf7
Reviewed-on: https://chromium-review.googlesource.com/827032
Commit-Queue: Mathieu Perreault <mathp@chromium.org>
Reviewed-by: Roger McFarlane <rogerm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#524214}

components/autofill/core/browser/ui/card_unmask_prompt_controller_impl.cc

@@ -117,7 +117,7 @@ void CardUnmaskPromptControllerImpl::OnVerificationResult(
 void CardUnmaskPromptControllerImpl::OnUnmaskDialogClosed() {
   card_unmask_view_ = nullptr;
   LogOnCloseEvents();
-  if (delegate_.get())
+  if (delegate_)
     delegate_->OnUnmaskPromptClosed();
 }
 
@@ -208,7 +208,10 @@ void CardUnmaskPromptControllerImpl::OnUnmaskResponse(
     pending_response_.should_store_pan = false;
   }
 
-  delegate_->OnUnmaskResponse(pending_response_);
+  // There is a chance the delegate has disappeared (i.e. tab closed) before the
+  // unmask response came in. Avoid a crash.
+  if (delegate_)
+    delegate_->OnUnmaskResponse(pending_response_);
 }
 
 void CardUnmaskPromptControllerImpl::NewCardLinkClicked() {