[Suggest] Fix undefined uint32 right-shift behavior in the transaction window

uint32 a = 0xffffffff;
a >= 32;
This is undefined behavior in C/C++. To prevent it from being optimized away cause hang or transaction window failure

now:
window >>= num_empty_slots;
fix:
window = num_empty == 32 ? 0 : window >> num_empty_slots;