Fix AddAccountSettings memory leak

The memory leak will always occur in AddAccoutSettings
when a null Bundle is returned in the addAccount we implement.

Bug: https://issuetracker.google.com/issues/65322371


Test: Install the app through the github i have offered in above link,
then press the "Test" item in ChooseAccountActivity (adb shell am start -n
'com.android.settings/.accounts.ChooseAccountActivity') serveal times.
Check the activity number by "adb shell dumpsys meminfo com.android.settings".

Change-Id: I3f139fe059e6094e9e5bf1660946ebc8bab6d090
Signed-off-by: tiansiming <tiansiming@xiaomi.com>