Incorrect HIR pretty printing for `if` / `else`

[tmiasko]

For example:

pub fn f(x: usize) {
    if x == 1 {
    } else if x == 2 {
    } else if x == 3 {
    } else if x == 4 {
    } else {
    }
}

is formatted as follows (this is complete output):

$ rustc --crate-type=lib a.rs -Zunpretty=hir
#[prelude_import]
use ::std::prelude::rust_2015::*;
#[macro_use]
extern crate std;
pub fn f(x:
             usize) {
                        if x == 1
                           {
                           } else if x == 2
                            {
                            }

[756445638]

mine looks like this

[yuyang@localhost src]$ rustc --crate-type=lib main.rs -Zunpretty=hir 
#[prelude_import]
use ::std::prelude::v1::*;
#[macro_use]
extern crate std;
pub fn f(x:
             usize) {
                        if x == 1
                           {
                           } else if x == 2
                            {
                            } else if x == 3 { } else if x == 4 { } else { } }


                                fn main() { }

not pretty but correct

[tmiasko]

With an extra main function there is enough output to reach the margin and print part of the output.

The problem is with formatting boxes,that are opened but never closed again. This is also the reason behind ever increasing indentation.