Allow Calendar.getInstance to be called with a null Locale.

LocaleData.get was changed to throw for null locales instead
of falling back to the default, so we need to adjust callers
accordingly.

Turns out all other callers would've thrown anyway (for different
reasons) so this change makes those exceptions explicit and
adds tests for them.

bug: 16938922
Change-Id: I3e77435a6b414b002b96a4f8deb44b51591c5a51