Node hangs while recomputing final_state caches

[Leo-Besancon]

During some cycles, the function get_cycle_history_cycles() in pos_final_state, used to recompute the pos caches after bootstrap, never seems to return.
The while let loop seems to never stop (for instance I printed the found cycles and it went 509, 510, 511, 512, 513, 514, 515, 509...).

This is because the code for get_cycle_history_cycles() assumes the serialized keys order increase with the cycle. It is not true, e.g. the key for cycle 509 is greater than the key for cycle 513 in lexicography order.