[SYCL][L0] Always set CommandList in _pi_context::getAvailableCommandList (#4359)

When adding a command list from the cache to the map, we were not returning
the newly-inserted element via `CommandList` reference.

Thus, the _pi_context::getAvailableCommandList function was returning
`PI_SUCCESS`, but `CommandList` was left uninitialized, leading to a
segfault when the command list is used later (in my case, in `enqueueMemFillHelper`).

Introduced in PR #4248.

Author: al42and

sycl/plugins/level_zero/pi_level_zero.cpp

@@ -876,7 +876,11 @@ pi_result _pi_context::getAvailableCommandList(
 
         ze_fence_handle_t ZeFence;
         ZE_CALL(zeFenceCreate, (ZeCommandQueue, &ZeFenceDesc, &ZeFence));
-        Queue->CommandListMap[ZeCommandList] = {ZeFence, true, CopyQueueIndex};
+        CommandList =
+            Queue->CommandListMap
+                .emplace(ZeCommandList,
+                         pi_command_list_info_t{ZeFence, true, CopyQueueIndex})
+                .first;
       }
       ZeCommandListCache.pop_front();
       return PI_SUCCESS;