Properly test for the existance of a client certificate

rowbot

@@ -26,7 +26,7 @@ die() {
   # This is a wrapper around printf so the format string isn't known ahead of
   # time.
   # shellcheck disable=SC2059
-  printf "$fmt\n" "$@" >&2
+  printf "FATAL: $fmt\n" "$@" >&2
   exit "${STATUS:-42}"
 }
 
@@ -280,7 +280,7 @@ on_first_002_net() {
 
     # This is a false positive
     # shellcheck disable=SC2102
-    if [[ -v config[client-cert] ]]; then
+    if [[ ${config[client-cert]} ]]; then
       if [[ ! -f ${config[client-cert]} ]]; then
         die "client certificate not found: %s" "${config[client-cert]}"
       fi