atomic_init instead of memset in c_factors.c

[pdav]

Hi,
in my understanding, initialization of tally in line 75 of c_factors.c is not C11-compliant:

• if initialized with memset, length of area to set to 0 should be sizeof (_Atomic long int) and not sizeof (long int)
• I bet that initializing an atomic variable with memset gives an undefined behaviour according to C11. I think you should individually initalize each array element with atomic_init