05873bb6b1tweak_add: fix API doc for tweak=0 (Jonas Nick) Pull request description: ACKs for top commit: real-or-random: ACK05873bb6b1Tree-SHA512: ef587a680c3355c6328dd61e0f5fcac80ea995f6045b4392fe35f3ee1c04ee1bd941662c120758ad641588670c1f0f53bfb17a802821f54100f1385b8bb7375a