Address strncat gcc8 warning in TSystem.cxx
Address strncat gcc8 warning in TSystem.cxx

The warning:

core/base/src/TSystem.cxx:1149:14: warning: ‘char* strncat(char*, const char*, size_t)’ accessing 1 byte at offsets 0 and [-2147483647, 2147483648] may overlap 1 byte at offset [0, 2147483649] [-Wrestrict]
       strncat(buff, c+1, n);
       ~~~~~~~^~~~~~~~~~~~~~

is wrong because gcc8 does not (can not) detect that the input is already trimmed to kBufSize [strlcat(inp, c, kBufSize);]
and that the buffer is also used in a segmented way (4 portion of kBufSize each).

Switch from strncat to strlcat to suppress the warning.
Add an assert expressing the known precondition.

karies/root,root-mirror/root,olifre/root,karies/root,karies/root,olifre/root,olifre/root,root-mirror/root,root-mirror/root,karies/root,olifre/root,root-mirror/root,karies/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,olifre/root,root-mirror/root,karies/root,olifre/root,karies/root,root-mirror/root,karies/root,karies/root,karies/root,olifre/root,karies/root,root-mirror/root,olifre/root,root-mirror/root,olifre/root,root-mirror/root