On Windows 7, there is yy/mm/dd'('ddd')' as short date format of Japanese.
When selecting this, ddd isn't converted to day of the week correctly.
FindInReadable will update start position iterator even if not found. So when
using FindInReadable again, we have to reset start position iterator.
MozReview-Commit-ID: AoS1Txq3Twc
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extra : rebase_source : 2f02189d0288e833debb2d4ca47efbca632924e5
717646428c