strptime: fix signed overflow
strptime: fix signed overflow

Return 0 if signed integer overflows occur

Fixes: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=47092

Signed-off-by: David Korczynski <aa743a0aaec8f7d7a1f01442503957f4d7a2d634@adalogics.com>

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