rt_sigprocmask not failing for bad address

DR's handling of `rt_sigprocmask` doesn't fail even if a bad address is passed. `handle_sigprocmask` indeed checks whether the passed address is valid: https://github.com/DynamoRIO/dynamorio/blob/223213a2f254640cd1433a48cf0bebd20f828274/core/unix/signal.c#L2306, but it returns success anyway: https://github.com/DynamoRIO/dynamorio/blob/223213a2f254640cd1433a48cf0bebd20f828274/core/unix/os.c#L7349. This is causing an assertion to fail in a proprietary app.