Usage Settings: Fix NPE when subscriberId is Null.

For mobile, a old API: buildTemplateMobileAll doesn't includes the
merged wifi network, call the new API: buildTemplateCarrierMetered
to replace the old one.

But new API: buildTemplateCarrierMetered requires non-null subscriberId.
Call old API: buildTemplateMobileAll when subscriberId is NULL since
the matched result is always empty when subscriberId is NULL. No any different
between buildTemplateCarrierMetered and buildTemplateMobileAll.

Bug: 190233044
Bug: 190135429
Test: make RunSettingsRoboTests -j ROBOTEST_FILTER=DataUsageUtilsTest
Change-Id: I3c7166e60e32142d5995d41722955dd54c21938f