Fix HasResult method of LTemplateInstruction to properly handle LCheckSmi

Fix HasResult method of LTemplateInstruction to properly handle LCheckSmi

LCheckSmi sometimes has a result register and sometimes not, even though its
LTemplateInstruction alwasys has room for one. Debug output use HasResult to
determine whether it was ok to de-ref result(), but HasResult doesn't check for
the case where LTemplateInstruction has a result but it's NULL.

R=svenpanne@chromium.org

Committed: http://code.google.com/p/v8/source/detail?r=15931

[danno, 2013-07-29 10:58:10]

PTAL

[Sven Panne, 2013-07-29 11:53:00]

LGTM. One can perhaps guard set_result() and result() with ASSERTs that the NULL
case doesn't happen, but I'll leave it up to you.

[danno, 2013-07-29 11:56:30]

Unfortunately, allowing NULL as a value result of CheckSmi seems to be baked in,
it appears to be important for some performance situations in register
allocation. That looked to be a bigger cleanup, so for now I just want to make
sure that debug output doesn't cause a SEGV.

[danno, 2013-07-29 11:57:52]

Committed patchset #1 manually as r15931 (presubmit successful).