surrogate characters in UTF16 into the replacement character 0xfffd, as we
find that this breaks some software.
FossilOrigin-Name: 4218c7b71fb6b227dbe4b852718584c150164af2d84e067cb810aa602554a609
UTF16 input buffer if the last two bytes of the UTF16 happen to be the
first half of a surrogate pair. Ticket [3fe897352e]
FossilOrigin-Name: 19064d7cea838e1a93fe63743ed247f440679e97