[SYCL] Handle nullptr arguments in level_zero (#6464)

* [SYCL] Handle nullptr arguments in level_zero

If specialization constant is not used on device, then the buffer for
it is not created on device side. In this case the host part passes nullptr
for the corresponding kernel operand holding the reference to the buffer
with constants.
This patch fixes the level_zero arguments handling to avoid SegFault
in the plugin.

Signed-off-by: Vyacheslav N Klochkov <vyacheslav.n.klochkov@intel.com>

Author: v-klochkov

sycl/plugins/level_zero/pi_level_zero.cpp

@@ -4976,8 +4976,11 @@ pi_result piextKernelSetArgMemObj(pi_kernel Kernel, pi_uint32 ArgIndex,
   //       piextKernelSetArgMemObj.
   //
   std::scoped_lock Guard(Kernel->Mutex);
+  // The ArgValue may be a NULL pointer in which case a NULL value is used for
+  // the kernel argument declared as a pointer to global or constant memory.
+  auto Arg = ArgValue ? *ArgValue : nullptr;
   Kernel->PendingArguments.push_back(
-      {ArgIndex, sizeof(void *), *ArgValue, _pi_mem::read_write});
+      {ArgIndex, sizeof(void *), Arg, _pi_mem::read_write});
 
   return PI_SUCCESS;
 }
@@ -5201,9 +5204,13 @@ piEnqueueKernelLaunch(pi_queue Queue, pi_kernel Kernel, pi_uint32 WorkDim,
 
   // If there are any pending arguments set them now.
   for (auto &Arg : Kernel->PendingArguments) {
-    char **ZeHandlePtr;
-    PI_CALL(
-        Arg.Value->getZeHandlePtr(ZeHandlePtr, Arg.AccessMode, Queue->Device));
+    // The ArgValue may be a NULL pointer in which case a NULL value is used for
+    // the kernel argument declared as a pointer to global or constant memory.
+    char **ZeHandlePtr = nullptr;
+    if (Arg.Value) {
+      PI_CALL(Arg.Value->getZeHandlePtr(ZeHandlePtr, Arg.AccessMode,
+                                        Queue->Device));
+    }
     ZE_CALL(zeKernelSetArgumentValue,
             (Kernel->ZeKernel, Arg.Index, Arg.Size, ZeHandlePtr));
   }