Fix some struct-tuple def prettyprint issues
- Removed space between struct name and parentheses
- Fixed indentation of the rest of the file (missing end)
- Don't print parentheses for structs with no fields
- Added test
auto merge of #5193 : sethpink/rust/struct-tup-pp, r=catamorphism

- Removed space between struct name and parentheses
- Fixed indentation of the rest of the file (missing end)
- Don't print parentheses for structs with no fields
- Added test