Format a git_oid into a buffer as a hex format c-string.
If the buffer is smaller than the size of a hex-formatted oid string plus an additional byte (GIT_OID_SHA_HEXSIZE + 1 for SHA1 or GIT_OID_SHA256_HEXSIZE + 1 for SHA256), then the resulting oid c-string will be truncated to n-1 characters (but will still be NUL-byte terminated).
If there are any input parameter errors (out == NULL, n == 0, oid == NULL), then a pointer to an empty string is returned, so that the return value can always be printed.
the buffer into which the oid string is output.
the size of the out buffer.
the out buffer pointer, assuming no input parameter errors, otherwise a pointer to an empty string.