Try to keep the behaviour from ea9f47a7 of erroring out if
unwinding ends up out of bounds (with pc==lr, where setting pc
to lr doesn't progress the unwind), but support unwinding from
functions without unwind info.
Signed-off-by: Martin Storsjo <martin@martin.st>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>