Lists_Add(): use size of destination when copying data

Lists_Add(): use size of destination when copying data

This fixes the following warning of clang:

/src/ngircd/lists.c:152:44:
 warning: size argument in 'strlcpy' call appears to be size of the
 source; expected the size of the destination [-Wstrlcpy-strlcat-size]

But it isn't a real problem, because the size of the source always is the
same than the size of the destination ...