am b38f8812: Prevent a NPE by checking mCallback.

* commit 'b38f88126b7ea255a884d06018d3d1c64e25bdff':
  Prevent a NPE by checking mCallback.
diff --git a/src/com/android/browser/DeviceAccountLogin.java b/src/com/android/browser/DeviceAccountLogin.java
index 818e076..8d734c2 100644
--- a/src/com/android/browser/DeviceAccountLogin.java
+++ b/src/com/android/browser/DeviceAccountLogin.java
@@ -107,8 +107,9 @@
         if (mTab.getDeviceAccountLogin() == null) {
             displayLoginUi();
         } else {
-            assert mCallback != null;
-            mCallback.loginFailed();
+            if (mCallback != null) {
+                mCallback.loginFailed();
+            }
         }
     }