Report intermediate expressions as errors in For next-exprs.

We weren't coercing the expression because we don't care about its type,
but that allowed intermediate-expressions to pass through without
reporting an error. Now we coerce the expression to its present type,
which will always fail if the type is disallowed and succeed otherwise.

Change-Id: Ic0de0d17f0f5d56360575efe992ce4d74dec2a5a
Bug: oss-fuzz:37620
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/441876
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
4 files changed