[x64] Rearrange code for OOB integer loads.

[x64] Rearrange code for OOB integer loads.

We cannot just clear the result register optimistically, because the
register allocator might assign the same register to result and buffer.

TEST=mjsunit/compiler/regress-445858
BUG=chromium:445858
LOG=y
R=jarin@chromium.org

Committed: https://crrev.com/cf866b7c612c25bace7d0f0ceb12456e5ad24d7f
Cr-Commit-Position: refs/heads/master@{#25950}

[Benedikt Meurer, 2015-01-02 09:45:15]

PTAL

[Jarin, 2015-01-02 09:52:02]

lgtm

[Benedikt Meurer, 2015-01-02 09:52:12]

The CQ bit was checked by bmeurer@chromium.org

[commit-bot: I haz the power, 2015-01-02 09:53:08]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/828303002/1

[commit-bot: I haz the power, 2015-01-02 10:15:32]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-02 10:15:46]

Patchset 1 (id:??) landed as
https://crrev.com/cf866b7c612c25bace7d0f0ceb12456e5ad24d7f
Cr-Commit-Position: refs/heads/master@{#25950}