Zero initialize tm struct.

[bradleybauer]

See here for what motivated this change.

[KjellKod]

This seems fine.

I'll go ahead and merge it and also like to call out that this is mostly a valgrind nonsense issue.
The difference is that with this fix all values are default initialized, vs previously the first value was zero initialized and the rest was default initialized.

This would yield identical outputs

    struct tm tm1{};
    std::cout 
        << "tm_sec: " << tm1.tm_sec << ", "
        << "\ntm_min: " << tm1.tm_min << ", "
        << "\ntm_hour: " << tm1.tm_hour << ", "
        << "\ntm_mday: " << tm1.tm_mday << ", "
        << "\ntm_mon: " << tm1.tm_mon << ", "
        << "\ntm_year: " << tm1.tm_year << ", "
        << "\ntm_wday: " << tm1.tm_wday << ", "
        << "\ntm_yday: " << tm1.tm_yday << ", "
        << "\ntm_isdst: " << tm1.tm_isdst << std::endl;
        
    struct tm tm2 = {0};
   std::cout 
        << "\ntm2\ntm_sec: " << tm2.tm_sec << ", "
        << "\ntm_min: " << tm2.tm_min << ", "
        << "\ntm_hour: " << tm2.tm_hour << ", "
        << "\ntm_mday: " << tm2.tm_mday << ", "
        << "\ntm_mon: " << tm2.tm_mon << ", "
        << "\ntm_year: " << tm2.tm_year << ", "
        << "\ntm_wday: " << tm2.tm_wday << ", "
        << "\ntm_yday: " << tm2.tm_yday << ", "
        << "\ntm_isdst: " << tm2.tm_isdst << std::endl;    
        

[KjellKod]

Fixing valgrind complaint. The fix is essentially a no-op change