We sometimes used to continue by jumping _back_ to the condition check at the
top of the loop. After my recent generator-related changes, that check is no
longer at the loop header, so a continue could create an additional loop. In
order to avoid this, we now always set the continue target to be the first
instruction following the loop body.

BUG=

Review-Url: https://codereview.chromium.org/1943383003
Cr-Commit-Position: refs/heads/master@{#36029}