Fix incorrect parse of statement macro followed by range

[dtolnay]

For the program fn main() { m! {} .. }, Syn would previously parse this as [Stmt::Expr(Expr::Range { start: Expr::Macro, end: None })]. The correct parse is [Stmt::Macro, Stmt::Expr(Expr::Range { start: None, end: None })] as is clear from the following diagnostic from rustc.

error[E0308]: mismatched types
 --> src/main.rs:1:19
  |
1 | fn main() { m! {} .. }
  |          -        ^^ expected `()`, found `RangeFull`
  |          |
  |          expected `()` because of default return type