ep_warmup_key_count becomes zero in case of corrupted access.log.old file and no access.log file

Steps To Reproduce:-
1) Load 10000 items on default bucket of two node cluster
2) Run access scanner and wait for access.log to get created.
3) open and corrupted the access.log file.
4) stop and start the server
collected the cbstats as :-
ep_warmup: enabled
ep_warmup_access_log: corrupt
ep_warmup_dups: 0
ep_warmup_estimated_item_count: unknown
ep_warmup_estimated_warmup_count: unknown
ep_warmup_key_count: 60000
ep_warmup_keys_time: 737179
ep_warmup_min_item_threshold: 100
ep_warmup_min_memory_threshold: 100
ep_warmup_oom: 0
ep_warmup_state: done
ep_warmup_thread: complete
ep_warmup_time: 1663848
ep_warmup_value_count: 60000
5) Load new set of 10,000 items
6) Run the access scanner, corrupted log file will become access.log.old and new access.log will get created
7) delete the access.log file
8) Stop and Start the server
collected the cbstats
ep_warmup: enabled
ep_warmup_dups: 0
ep_warmup_estimated_item_count: unknown
ep_warmup_estimated_warmup_count: unknown
ep_warmup_key_count: 0
ep_warmup_keys_time: 900
ep_warmup_min_item_threshold: 100
ep_warmup_min_memory_threshold: 100
ep_warmup_oom: 0
ep_warmup_state: done
ep_warmup_thread: complete
ep_warmup_time: 1041
ep_warmup_value_count: 0