A sloppy function in a block scope implicitily creates a var in the outer
declaration scope if it's not blocked. The assignment created reads the local
lexical declaration for the function. The reference introduced automatically
takes part in NeedsHoleCheck, requiring the reference to have a valid position.
Since the assignment will happen after the local declaration, we give the
end_position() of the closure as the position of the reference, so hole checks
can be omitted.

Bug: chromium:917755
Change-Id: Iee0e042b2463f97f05075f9eec09dac8c6eaf539
Reviewed-on: https://chromium-review.googlesource.com/c/1408991Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58823}