optim: don't `getScriptSnapshot` when we already have the snapshot

[agilgur5]

Summary

Tiny one-line optimization: getScriptSnapshot was called when we already have the snapshot

Details

• the snapshot is set above, so no need to get it
• also the snapshot from above is used below already, so this doesn't seem to be intentional
  • it originates from https://github.com/ezolenko/rollup-plugin-typescript2/commit/2d330640316894752bae5ae64d94bc90652e4564#diff-a2a171449d862fe29692ce031981047d7ab755ae7f84c707aef80701b3ea0c80R197 which similarly doesn't seem intentional