`&` doesn't always work in `if` statement

[bbrk24]

For some reason, these generate invalid JS:

if & then x         // $ => if ($) x
return if & then x  // $ => return ($ ? x : void 0)

While these do not:

foo if & then x   // foo(($) => ($ ? x : void 0))
f := if & then x  // const f = ($) => ($ ? x : void 0)

[Erik Demaine]

return if & then x is fixed via #1177.

The issue with if & then x is that it's an if statement instead of an expression. I guess in these situations we need to unbare the block (add braces) and call insertReturn. An example where this is actually useful:

=>
  if & then y

Playground link