This fixes ExceptionContinueExecution cases, where we want to continue execution on the original context (or as modified by the handler), not on some halfway unwinded one.
This can fail on optimized builds, where functions can end after a noreturn function call without an epilog / ret, but with an int 3. We simply fail gracefully, which is the right thing to do.
RtlpCaptureNonVolatileContextPointers walks the stack and captures the addresses of all non-volatile registers on the stack, when they have been saved first. This is needed to be able to fix up the non-volatile on a system call, which doesn't capture non-volatiles, but relies on them to be restored by the callees.
Instead of only checking for the TargetFrame, also check for a mode change, i.e. RIP went from kernel to user, in which case the target frame was not reached yet, because it was too large, but processing can't continue here.
RtlSetUnwindContext uses RtlpCaptureNonVolatileContextPointers to set the non-volatile registers in the the stack. They will be picked up, when returning back or unwinding, e.g. to the system call handler.
