The bounds check in LoadDataSegment was off by one. I also improved the
error message, and fixed an issue where data was initialized even if
the bounds check failed.

In InstantiateModuleForTesting I allow instantiation of modules without
exports. This check was legacy code from the time where instantiation
and execution was still combined in a single function.

R=titzer@chromium.org, rossberg@chromium.org
TEST=cctest/test-run-wasm-module/InitDataAtTheUpperLimit

Review-Url: https://codereview.chromium.org/2486183002
Cr-Commit-Position: refs/heads/master@{#40856}