Inconsistent NUL-(non)termination of zero-sized buffers by strnzcpyn (misc.c)

unlike the other strnz* type copy functions in misc.c, if size is 0 for this function, the dst pointer does not get null terminated. It is either a bug in this function, OR it is a bug in all the other functions (which do null terminate is size is 0).

I believe usage for all functions is this:

char buf[SIZE+1];
strnzcpy(buf, some_data, SIZE);

and that being the convension, then a 0 size SHOULD null terminate, and the strnzcpyn function should also null terminate in that case.

I listed this as a bug, (it almost certainly is). Just not sure which function the bug is in (likely it is in strnzcpyn). I think I was the one that originally wrote the strnzcpyn (due to a need for tacking size of data written), and I simply F'd this one up.

Start in misc.c by comparing strnzcpyn with the other strnz* copy functions, focusing on their behavior when size is zero. Determine which behavior matches the stated buffer convention, then verify that the chosen behavior is consistent across the functions and that the zero-sized destination is handled correctly.