>>> I tried testing it out too. There is a patch where the third hunk doesn't
>>> apply (errors with "can't find the text to patch" in regular usage). This
>>> command ends with cryptic "No next hunk".
>> This is what I expected that diff-hunk-next might signal an error
>> that we should catch, but still couldn't find a patch that fails
>> with such error.  So I will try to construct such a patch manually.
>
> Try the patch attached to this message:
> https://debbugs.gnu.org/cgi/bugreport.cgi?bug=63896#5

Thanks, I forgot about signatures in git patches.
diff-mode already handles them in diff-fixup-modifs:

                        ;; In git format-patch "^-- $" signifies
                        ;; the end of the patch.
			(and (eq diff-buffer-type 'git)
			     (looking-at "^-- $"))

So I just copied this code here: