OSV-2020-669 Use-of-uninitialized-value in g_date_time_get_week_number

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=17648 Crash type: Use-of-uninitialized-value Crash state: gdatetimegetweeknumber gdatetimenewweek parseisoNUMBERdate...