fix hires fix not working in API when user does not specify upscaler

    def sample(self, conditioning, unconditional_conditioning, seeds, subseeds, subseed_strength, prompts):

        self.sampler = sd_samplers.create_sampler(self.sampler_name, self.sd_model)

        latent_scale_mode = shared.latent_upscale_modes.get(self.hr_upscaler, None) if self.hr_upscaler is not None else shared.latent_upscale_default_mode

        latent_scale_mode = shared.latent_upscale_modes.get(self.hr_upscaler, None) if self.hr_upscaler is not None else shared.latent_upscale_modes.get(shared.latent_upscale_default_mode, "nearest")

        if self.enable_hr and latent_scale_mode is None:

            assert len([x for x in shared.sd_upscalers if x.name == self.hr_upscaler]) > 0, f"could not find upscaler named {self.hr_upscaler}"