include/servtree.h: fix null pointer dereference

svs can be NULL when we are logging /stats <letter> services. so check
for that case before looking up ->logtarget.
chanserv: Don't allow kick or deop on services.

Also add an error message, and allow opping services (should have no
effect).
Merge branch 'bugfix-1' of https://github.com/ilbelkyr/atheme