dateseq abnormal termination when it receives an invalid date format

[HyeonseopJeong]

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Hi, I found that dateseq (version 0.4.7.git10.3793f3b) abnormally terminates when it receives "0B" for where "Month" is supposed to be.

Example :

$ dateseq 2020-0B-01 2020-09-28

Assertion failed: ((signed int)md - 28 >= 0), function __get_bdays, file ./bizda.c, line 279.
Aborted


$ dateseq 2020-09-01 2020-0B-28

Assertion failed: ((signed int)md - 28 >= 0), function __get_bdays, file ./bizda.c, line 279.
Aborted

I found this failure with AFL fuzzer.

Please let me know if you need more information for reproducing this. Thanks.