2013-01-18  Sharath Kamath  <kamath.sharath@gmail.com>

        WebCLProgram::finishCallback conformance test crashes.
        Issue #77

        Reviewed by Antonio.

        When WebCLProgram::build() api is called with a callback event.
        The call back is not registered and thus the static cast fails.
        Adding null check on the pointer to avoid crash if static fails due to other issues.

        * Modules/webcl/WebCLProgram.cpp:
        (WebCore::WebCLProgram::finishCallback): Add null check.
        (WebCore::WebCLProgram::build): Register the object into file level static for use in finishCallback.