Avoid potential UCollator leak for older ICU versions.
ICU versions 53 and earlier rely on icu_set_collation_attributes() to
process the attributes in the locale string. Avoid leaking the
already-opened UCollator object if an error is encountered.
Discussion: https://postgr.es/m/
04182066-7655-344a-b8b7-
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Reviewed-by: Peter Eisentraut