Remove undefined variable usage
merged branch ftassi/remove-extension-name-from-exception (PR #1138)

This PR was merged into the master branch.

Discussion
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Remove undefined variable usage

See https://github.com/fabpot/Twig/commit/44873875ff6ca50c654e3bd28fe19b7ce5108f42#L1R728

Commits
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71d7d50 Remove undefined variable usage