Fix zip file entry resolution on Windows.
Fix zip file entry resolution on Windows.

See also https://github.com/google/j2cl/issues/9.

Fixes https://github.com/google/closure-compiler/pull/3206.
Closes https://github.com/google/closure-compiler/pull/3207.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=230635801

google/closure-compiler,vobruba-martin/closure-compiler,nawawi/closure-compiler,monetate/closure-compiler,ChadKillingsworth/closure-compiler,nawawi/closure-compiler,vobruba-martin/closure-compiler,ChadKillingsworth/closure-compiler,google/closure-compiler,ChadKillingsworth/closure-compiler,monetate/closure-compiler,Yannic/closure-compiler,monetate/closure-compiler,Yannic/closure-compiler,Yannic/closure-compiler,monetate/closure-compiler,vobruba-martin/closure-compiler,nawawi/closure-compiler,ChadKillingsworth/closure-compiler,Yannic/closure-compiler,vobruba-martin/closure-compiler,google/closure-compiler,nawawi/closure-compiler,google/closure-compiler