Fix: alerts: ensure sample alert agents handle undefined recipient

extra/alerts/alert_file.sh.sample

@@ -33,8 +33,19 @@
 #   </alerts>
 # </configuration>
 
+# No one will probably ever see this echo, unless they run the script manually.
+# An alternative would be to log to the system log, or similar. (We can't send
+# this to the configured recipient, because that variable won't be defined in
+# this case either.)
 if [ -z $CRM_alert_version ]; then
-    echo "Pacemaker version 1.1.15 or later is required" >> "${CRM_alert_recipient}"
+    echo "$0 must be run by Pacemaker version 1.1.15 or later"
+    exit 0
+fi
+
+# Alert agents must always handle the case where no recipients are defined,
+# even if it's a no-op (a recipient might be added to the configuration later).
+if [ -z "${CRM_alert_recipient}" ]; then
+    echo "$0 requires a recipient configured with a full filename path"
     exit 0
 fi
 

extra/alerts/alert_snmp.sh.sample

@@ -43,7 +43,12 @@
 # ================================
 
 if [ -z "$CRM_alert_version" ]; then
-    echo "Pacemaker version 1.1.15 or later is required"
+    echo "$0 must be run by Pacemaker version 1.1.15 or later"
+    exit 0
+fi
+
+if [ -z "$CRM_alert_recipient" ]; then
+    echo "$0 requires a recipient configured with the SNMP server IP address"
     exit 0
 fi