Add support for MNC=00

This adds support for operators with MNC (Mobile Network Code) zero
to add customized resources. For example, it makes it possible to
add a folder called "/res/values-mnc00/" in an application. This will
cause resources in that folder to be used when MNC is zero.
(There is a total of 14 countries that have an operator with MNC
zero.)

Without this fix, the resource framework gets confused, because MNC 0
is normally used when the MNC is undefined (not set).

Bug: 7170488
Change-Id: Icfd39fd0c739216e89446252ea0e7ceba6f002c6