[lldb] Don't call AddRemoteRegisters if the target XML did not include any registers (#96907)

Fixes #92541

When e69a3d18f48bc0d81b5dd12e735a2ec898ce64d added fallback register
layouts, it assumed that the choices were target XML with registers, or
no target XML at all.

In the linked issue, a user has a debug stub that does have target XML,
but it's missing register information.

This caused us to finalize the register information using an empty set
of registers got from target XML, then fail an assert when we attempted
to add the fallback set. Since we think we've already completed the
register information.

This change adds a check to prevent that first call and expands the
existing tests to check each architecture without target XML and with
target XML missing register information.

0 files changed, 0 insertions, 0 deletions