The curse hit Harry only because he wanted so, if he tried to defend himself the curse would have bounced to Voldemort, but it didn´t half killed Harry, it wuould have killed him if it wasn´t for the blood protection. I think that the blood connection had to do with Voldemort´s fainting more than the Horcrux issue, but it can also be because the Elder Wand also backfired at the same time it hit Harry...don´t know.
Finally, the Cucriatus curse didn´t affect Harry, because he didn´t wanted to, and as being the true master of the Elder Wand he was the one at control.
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