Abort optimization in corner case.

The %OptimizeFunctionOnNextCall sledgehammer can cause a function to be
marked for optimization before it's ever been compiled by fullcode.
This can lead to the situation where a function doesn't have optimization
disabled until we try to compile it optimized.

Basically, the assert should just handle this case more gracefully.

R=yangguo@chromium.org
BUG=436893
LOG=Y

Review URL: https://codereview.chromium.org/760063002

Cr-Commit-Position: refs/heads/master@{#25528}