Also adding curly braces to expressions other than conditional statements

Since we change 
```r
if (TRUE)
  return(call(a))
```
Into 
```r
if (TRUE) {
  return(call(a))
}
```
We should probably also change 
```r
while (FALSE)
  xyz(v)
```
Into
```r
while (FALSE) {
  xyz(v)
}
```

Reference: https://github.com/r-lib/styler/pull/279#discussion_r151879108