Kill another analyzer warning in javascriptcore
https://bugs.webkit.org/show_bug.cgi?id=110802

Reviewed by Benjamin Poulain.

Add null checks.

* profiler/LegacyProfiler.cpp:
(JSC::LegacyProfiler::startProfiling):
(JSC::LegacyProfiler::stopProfiling):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144026 268f45cc-cd09-0410-ab3c-d52691b4dbfc