2013-09-05  Shilpa Shri  <shilpa.shri@samsung.com>

        Negative values for rowPitch and slicePitch crashes safari.
        Issue #284

        Sending a negative value to rowPitch and/or slicePitch calculates a negative offset.
        This tries to read/write from buffer out of bounds and thus API which uses this causes crash.
        This is not handled by OpenCL. So WebCL needs to add a check for rowPitch being positive.

        Reviewed by Antonio.

        Following conformance test files are fixed:
        conformance/buffimgs/cl_commandQueue_enqueueWriteBufferRect.html
        conformance/buffimgs/cl_commandQueue_enqueueReadImage.html
        conformance/buffimgs/cl_commandQueue_enqueueReadBufferRect.html
        conformance/buffimgs/cl_commandQueue_enqueueWriteImage.html
        conformance/buffimgs/cl_commandQueue_enqueueCopyBufferRect.html

        * Modules/webcl/WebCLCommandQueue.cpp:
        (WebCore::WebCLCommandQueue::enqueueWriteBufferRect):
        (WebCore::WebCLCommandQueue::enqueueReadImage):
        (WebCore::WebCLCommandQueue::enqueueReadBufferRect):
        (WebCore::WebCLCommandQueue::enqueueWriteImage):
        (WebCore::WebCLCommandQueue::enqueueCopyBufferRect):