reopen the same cursor that was closed.

I previously changed it to call `input.close()` instead of `close()`: https://github.com/FoundationDB/sql-layer/pull/1595/files#diff-9199969a816e31d5119cee8b25a5ce26L370 but forgot to change the corresponding call to `open()` to be `input.open()`. 

It would be great to create a test that hits this that's not an MT, but I couldn't figure out how to get to that block of code.