ext/intl: Fix Locale::lookup() fallback on invalid language tags

[LamentXU123]

Locale::lookup() and locale_lookup() should return NUL when it fails. Now they returns the fallback locale even when lookup_loc_range() failed and set an intl error.

For example:

<?php

var_dump(Locale::lookup([''], 'de-DE', false, 'en-US'));
var_dump(intl_get_error_message());

var_dump(locale_lookup([''], 'de-DE', false, 'en-US'));
var_dump(intl_get_error_message());
?>

now returns

string(5) "en-US"
string(75) "lookup_loc_range: unable to canonicalize lang_tag: U_ILLEGAL_ARGUMENT_ERROR"
string(5) "en-US"
string(75) "lookup_loc_range: unable to canonicalize lang_tag: U_ILLEGAL_ARGUMENT_ERROR"

but I expect:

NULL
string(75) "lookup_loc_range: unable to canonicalize lang_tag: U_ILLEGAL_ARGUMENT_ERROR"
NULL
string(75) "lookup_loc_range: unable to canonicalize lang_tag: U_ILLEGAL_ARGUMENT_ERROR"