In InitializeZerothFrame check for a CFA/AFA or error out

There is a failure where we somehow get an invalid register
number being used to calculate the canonical frame address,
and this ends up with lldb crashing with a null deref because it
assumes that it is always able to find information about that
register.

This patch adds a check for a failure to get a register, and
declares the frame invalid in that case, with some additional
logging or an assert for debug builds.

Differential Revision: https://reviews.llvm.org/D143232
rdar://104428038