καὶ ὁ Ἀστυάγης δὲ ὅ τι δέοιτο αὐτοῦ ὁ Κῦρος οὐδὲν ἐδύνατο ἀντέχειν μὴ οὐ χαρίζεσθαι
The old commentary says that οὐδὲν depends on χαρίζεσθαι. I think it is wrong, and it is adverbial acc describing ἐδύνατο: with respect to nothing was he capable to withhold gratification.
οὐδὲν picks up the relative clause and then applies yes primarily to ἐδύνατο (“he was quite unable”) but still the sentence can legitimately be understood as saying that he couldn’t resist giving him any favor at all (extending the force of ουδεν to χαρίζεσθαι).