ResourcesManager: Return null on failure to create Resources

A lot of calling framework code expects a null value on failure,
and didn't catch the previous exception. There were some strange
corner cases where previously a null value was not checked for
in framework code, allowing the null Resources object to be
returned to the caller. Introducing an exception changed the
semantics and can crash certain apps.

Bug:30422475
Change-Id: I51d34ae43c9ec605a8790989c56cf85b815ff5b8