fmt: respect one-liner `if` expressions even when an `else` is present

[anderseknert]

Whether else should be moved to a line of its own at all is debatable, but I think the formatter at minimum should respect simple one-liner constructs when else is involved:

This:

foo if input.bar else := false

Currently formats to this:

foo if input.bar

else := false

Which just makes the else look entirely detached from the if.