[UR][CUDA] Fix command-buffer handle inheritance

The `ur_exp_command_buffer_handle_t_` definition in the CUDA
adapter was missed in #17118 in
the changes to inherit from a base handle.

Discovered by seeing segfaults in the UR CTS tests locally, and
git bisecting back to that change.

Author: EwanC

unified-runtime/source/adapters/cuda/command_buffer.cpp

@@ -57,7 +57,7 @@ ur_result_t commandHandleDestroy(
 
 ur_exp_command_buffer_handle_t_::ur_exp_command_buffer_handle_t_(
     ur_context_handle_t Context, ur_device_handle_t Device, bool IsUpdatable)
-    : Context(Context), Device(Device), IsUpdatable(IsUpdatable),
+    : handle_base(), Context(Context), Device(Device), IsUpdatable(IsUpdatable),
       CudaGraph{nullptr}, CudaGraphExec{nullptr}, RefCount{1},
       NextSyncPoint{0} {
   urContextRetain(Context);

unified-runtime/source/adapters/cuda/command_buffer.hpp

@@ -128,7 +128,7 @@ struct ur_exp_command_buffer_command_handle_t_ : ur::cuda::handle_base {
   command_data_type_t CommandData;
 };
 
-struct ur_exp_command_buffer_handle_t_ {
+struct ur_exp_command_buffer_handle_t_ : ur::cuda::handle_base {
 
   ur_exp_command_buffer_handle_t_(ur_context_handle_t Context,
                                   ur_device_handle_t Device, bool IsUpdatable);