[Payments] Do not update UI if it is null

This could happen when show has not been called,

Bug: 721362
Change-Id: I1bae92bbf87c9ccc63326d4d1ffd7c798cb4aadc
Reviewed-on: https://chromium-review.googlesource.com/968708Reviewed-by: Rouslan Solomakhin <rouslan@chromium.org>
Commit-Queue: Ganggui Tang <gogerald@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544042}

chrome/android/java/src/org/chromium/chrome/browser/payments/PaymentRequestImpl.java

@@ -1525,7 +1525,10 @@ public class PaymentRequestImpl
         mPaymentMethodsSection.addAndSelectOrUpdateItem(updatedAutofillPaymentInstruments);
 
         updateInstrumentModifiedTotals();
-        mUI.updateSection(PaymentRequestUI.TYPE_PAYMENT_METHODS, mPaymentMethodsSection);
+
+        if (mUI != null) {
+            mUI.updateSection(PaymentRequestUI.TYPE_PAYMENT_METHODS, mPaymentMethodsSection);
+        }
     }
 
     @Override
@@ -1536,7 +1539,10 @@ public class PaymentRequestImpl
         mPaymentMethodsSection.removeAndUnselectItem(guid);
 
         updateInstrumentModifiedTotals();
-        mUI.updateSection(PaymentRequestUI.TYPE_PAYMENT_METHODS, mPaymentMethodsSection);
+
+        if (mUI != null) {
+            mUI.updateSection(PaymentRequestUI.TYPE_PAYMENT_METHODS, mPaymentMethodsSection);
+        }
     }
 
     /**