[compiler] Conditional expressions probably need to return undefined by default #45

Problem

x = if false: 1
// x === null

y = (->
  if false:
    1
)()
// y === undefined

Wrapping an expression in a function had better not change its value.

Proposed Solution

While trying to work around JavaScript's proliferation of distinct-yet-falsy values may be noble in spirit, the fact that JavaScript returns undefined by default basically forces LSC to do the same for consistency's sake. I think unprovided branches of conditional expressions (if, and possibly match if it doesn't throw-on-else) should be returning undefined to match up with JavaScript core function behavior.