zsh:z{profile,logout}: Kill only 'own' ssh-agent

Kill the ssh-agent only if it was created in this session.

Like that the login shell can inherit SSH_AGENT_PID without it killing
the agent at the end. For this to work properly it is important that
LAUNCHED_SSH_AGENT is not exported, otherwise nested login shells will
mess with each other.

.config/zsh/.zlogout

@@ -1 +1,2 @@
-[[ -z $SSH_AGENT_PID ]] || kill "$SSH_AGENT_PID"
+# Kill ssh-agent if it was created in this session
+! (( LAUNCHED_SSH_AGENT && SSH_AGENT_PID )) || kill "$SSH_AGENT_PID"

.config/zsh/.zprofile

@@ -48,6 +48,8 @@ fi
 # SSH
 if (( $+commands[ssh-agent] )) && [[ ! $SSH_AGENT_PID ]]; then
 	eval "$(ssh-agent)" >/dev/null
+	# See .zlogout
+	LAUNCHED_SSH_AGENT=1
 fi
 
 # Editor