Segger Systemview calls k_current_get() in sys_trace_k_thread_switched_in.
During early boot, this hook is triggered while k_is_pre_kernel() is true.
This triggers an assertion failure when CONFIG_ASSERT is enabled.
Add a guard to ignore the thread switch event if it is called pre-kernel.
Signed-off-by: Igor Knippenberg <knippenberg@filics.eu>