gfxstream: guest: vk_CmdBeginTransformFeedbackEXT fix

pCounterBuffers can be NULL, which crashes on the autogen path:

"For each element of pCounterBuffers that is VK_NULL_HANDLE,
transform feedback will start capturing vertex data to byte zero
in the corresponding bound transform feedback buffer."

Need to special case.

     Intel

Reviewed-by: Aaron Ruby <aruby@blackberry.com>
Acked-by: Yonggang Luo <luoyonggang@gmail.com>
Acked-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27246>

src/gfxstream/codegen/scripts/cereal/functable.py

@@ -122,6 +122,8 @@ HANDWRITTEN_ENTRY_POINTS = [
     "vkResetCommandPool",
     "vkFreeCommandBuffers",
     "vkResetCommandPool",
+    # Transform feedback
+    "vkCmdBeginTransformFeedbackEXT",
     # Special cases to handle struct translations in the pNext chain
     # TODO: Make a codegen module (use deepcopy as reference) to make this more robust
     "vkAllocateMemory",