[Fix #689] Use GPG_AGENT_INFO instead of GPG_AGENT_PID

GPG_AGENT_PID may not be defined. Also, source gpg-agent.env before
checking the PID.

modules/gpg/init.zsh

@@ -15,11 +15,14 @@ _gpg_agent_conf="$HOME/.gnupg/gpg-agent.conf"
 _gpg_agent_env="${TMPDIR:-/tmp}/gpg-agent.env"
 
 # Start gpg-agent if not started.
-if ! ps -U "$USER" -o pid,ucomm | grep -q -- "${GPG_AGENT_PID:--1} gpg-agent"; then
-  eval "$(gpg-agent --daemon | tee "$_gpg_agent_env")"
-else
+if [[ -z "$GPG_AGENT_INFO" ]]; then
   # Export environment variables.
   source "$_gpg_agent_env" 2> /dev/null
+
+  # Start gpg-agent if not started.
+  if ! ps -U "$USER" -o pid,ucomm | grep -q -- "${${${(s.:.)GPG_AGENT_INFO}[2]}:--1} gpg-agent"; then
+    eval "$(gpg-agent --daemon | tee "$_gpg_agent_env")"
+  fi
 fi
 
 # Inform gpg-agent of the current TTY for user prompts.