Bug 1386666 - Remove try..catch(ex if ex) statements from toolkit/components/osfile/ so that ESLint can parse the files. r=mossop

MozReview-Commit-ID: 786dBxzN3Uc

--HG--
extra : rebase_source : bcd8bfa32c5d93f4559bda985521c3805b43c6b6